Number stories within 20
By the end of this chapter you will be able to
- Choose add or take away from a story
- Add numbers to make a total up to 20
- Take away from a number up to 20
- Check an answer by doing the opposite
- Write a number sentence to match a story
You should already know
- Adding and taking away within 10 (Chapter 8)
- Number bonds to 10 (Chapter 5)
Where this leads
- Shapes (Level 1, Chapter 10)
Step-by-step practice: maths (Level 1). Small steps, repeated until fluent. Content: Read a short story and decide whether to add or take away, Add and take away with totals up to 20, using counting on or back or a ten frame, Check an answer by doing the inverse, Write a number sentence to match a story.
Exercise P Do you remember?
Non-calculatorMethod. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.6
- Count on 3 more. We add 3 to 6.6 + 3
- Write the answer. 9
Check. Count on from the other number too. You get 9 both ways.
Watch out. Count on, do not start again from one.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.9
- Take away 4. Cross out or count back this many.9 - 4
- Write the answer. This is how many are left.5
Check. Add back: 5 + 4 = 9. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Find the missing part. Ask what goes with the known part to make the whole.
- Look at the whole and the part you know. The whole is 10 and the known part is 7.10 and 7
- Count on from the known part to the whole. Or take the known part away from the whole.10 - 7 = 3
- Write the missing part. 3
Check. Put the two parts back together: 7 and 3 make 10.
Watch out. The two parts always add up to the whole.
Method. More means add.
- Start with 4 pens. Tom had four pens.4
- Add the 2 more. Two more were given.4 + 2 = 6
- Write the answer. 6
Check. Count on 2 from 4: 5, 6. It works.
Watch out. More means add.
Method. Say the numbers in order and find the one after 14.
- Say the numbers. Count 13, 14, 15.13, 14, 15
- Find the number after 14. It is the next one in the count.15
- Write the answer. 15
Check. Count back from 15: 15, 14. It works.
Watch out. The number after 14 is one more than 14.
Add or take away?
Read the story. Ask: does the number get bigger or smaller?
Bigger means add. Smaller means take away.
Key ideas
- More, gets and found mean add.
- Some go, lost and given away mean take away.
- Read the whole story before you decide.
Method. Look at the story. Does the number get bigger?
- Find the start. Noah has 6 stickers.6
- Decide what happens. He is given more, so the number gets bigger.bigger
- Write the word. add
Check. 6 + 5 = 11. The number got bigger.
Watch out. Given more means add.
Method. Look at the story. Does the number get smaller?
- Find the start. Jack has 12 cards.12
- Decide what happens. Cards are lost, so there are fewer.smaller
- Write the words. take away
Check. 12 − 4 = 8. The number got smaller.
Watch out. Lost means take away.
Method. Look at the story. Does the number get bigger?
- Find the start. Mei has 9 shells.9
- Decide what happens. She finds more, so the number gets bigger.bigger
- Write the word. add
Check. 9 + 3 = 12. The number got bigger.
Watch out. Found more means add.
Watch out
Watch out. Words like “more” can be part of a take-away story. Check what happens to the number.
Exam tip
Grown-up tip. Read the story aloud. Ask: “Did we get more, or did some go?” Act out the story with objects before choosing.
Exercise 9A Add or take away?
Non-calculatorMethod. Read the story. Does the number get bigger or smaller?
- Find the start. Amira starts with 4.4
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Noah starts with 9.9
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Priya starts with 7.7
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Jack starts with 16.16
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Zainab starts with 10.10
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Leo starts with 6.6
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Mei starts with 7.7
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Tom starts with 6.6
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Aisha starts with 7.7
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Ruby starts with 20.20
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Amira starts with 11.11
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Noah starts with 20.20
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Priya starts with 14.14
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Jack starts with 18.18
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Zainab starts with 4.4
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Leo starts with 18.18
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Adding within 20
To add numbers up to 20, start at the bigger number and count on.
A ten frame helps. Fill the first frame to ten, then count the rest.
Key ideas
- Start at the bigger number.
- Count on the smaller number.
- A full ten frame makes ten. Count the rest.
Method. Start at the bigger number and count on.
- Start at 8. The bigger number is 8.8
- Count on 6. Nine, ten, eleven, twelve, thirteen, fourteen.9, 10, 11, 12, 13, 14
- Write the answer. 14
Check. 6 + 8 = 14. It is the same both ways.
Watch out. Count on, do not start again from one.
Method. Make ten first, then count the rest.
- Make ten. Take 3 from the 9 to make 7 + 3 = 10.7 + 3 = 10
- Count the rest. There are 6 left in the 9.10 + 6
- Write the answer. 16
Check. 9 + 7 = 16. It is the same both ways.
Watch out. Making ten makes adding easier.
Method. More means add.
- Start with 11. Ruby had eleven stamps.11
- Add the 5 more. Count on 5 from 11.11 + 5 = 16
- Write the answer. 16
Check. Count back 5 from 16: 15, 14, 13, 12, 11. It works.
Watch out. Count on from the bigger number.
Watch out
Watch out. Be careful when you cross ten. 14 is one ten and four, not 10 and 14.
Exam tip
Grown-up tip. Use two ten frames or two cups. Fill one to ten, then count the rest. Ask: “How many tens? How many more?”
Exercise 9B Adding within 20
Non-calculatorMethod. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.9
- Count on 9 more. We add 9 to 9.9 + 9
- Write the answer. 18
Check. Count on from the other number too. You get 18 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.11
- Count on 6 more. We add 6 to 11.11 + 6
- Write the answer. 17
Check. Count on from the other number too. You get 17 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.5
- Count on 5 more. We add 5 to 5.5 + 5
- Write the answer. 10
Check. Count on from the other number too. You get 10 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.12
- Count on 8 more. We add 8 to 12.12 + 8
- Write the answer. 20
Check. Count on from the other number too. You get 20 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.7
- Count on 6 more. We add 6 to 7.7 + 6
- Write the answer. 13
Check. Count on from the other number too. You get 13 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.8
- Count on 6 more. We add 6 to 8.8 + 6
- Write the answer. 14
Check. Count on from the other number too. You get 14 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.11
- Count on 5 more. We add 5 to 11.11 + 5
- Write the answer. 16
Check. Count on from the other number too. You get 16 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.15
- Count on 3 more. We add 3 to 15.15 + 3
- Write the answer. 18
Check. Count on from the other number too. You get 18 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.14
- Count on 5 more. We add 5 to 14.14 + 5
- Write the answer. 19
Check. Count on from the other number too. You get 19 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.13
- Count on 5 more. We add 5 to 13.13 + 5
- Write the answer. 18
Check. Count on from the other number too. You get 18 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.15
- Count on 4 more. We add 4 to 15.15 + 4
- Write the answer. 19
Check. Count on from the other number too. You get 19 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.10
- Count on 6 more. We add 6 to 10.10 + 6
- Write the answer. 16
Check. Count on from the other number too. You get 16 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.8
- Count on 6 more. We add 6 to 8.8 + 6
- Write the answer. 14
Check. Count on from the other number too. You get 14 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.15
- Count on 3 more. We add 3 to 15.15 + 3
- Write the answer. 18
Check. Count on from the other number too. You get 18 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.14
- Count on 3 more. We add 3 to 14.14 + 3
- Write the answer. 17
Check. Count on from the other number too. You get 17 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.12
- Count on 6 more. We add 6 to 12.12 + 6
- Write the answer. 18
Check. Count on from the other number too. You get 18 both ways.
Watch out. Count on, do not start again from one.
Taking away within 20
To take away from a number up to 20, start at the bigger number. Count back, one at a time.
You can count back the first part to ten, then count back the rest.
Key ideas
- Start at the number you take from.
- Count back the number taken away.
- The answer is what is left.
Method. Start at 15 and count back 3.
- Start at 15. This is the number we take from.15
- Count back 3. Fourteen, thirteen, twelve.14, 13, 12
- Write the answer. 12
Check. 12 + 3 = 15. It works.
Watch out. Count back, to the left.
Method. Count back 5 from 18, one step at a time.
- Start at 18. This is the number we take from.18
- Count back 5. Seventeen, sixteen, fifteen, fourteen, thirteen.17, 16, 15, 14, 13
- Write the answer. 13
Check. 13 + 5 = 18. It works.
Watch out. Count the jumps, not the numbers you say.
Method. Take away the 6 that break.
- Start with 14. Mei has fourteen pencils.14
- Take away 6. Six break, so take them away.14 - 6 = 8
- Write the answer. 8
Check. 8 + 6 = 14. It works.
Watch out. Take away the ones that break.
Watch out
Watch out. Count back, not on. 15 − 3 is 12, not 18.
Exam tip
Grown-up tip. Use a number line from 0 to 20. Start at the number and move left, one step at a time.
Exercise 9C Taking away within 20
Non-calculatorMethod. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.16
- Take away 7. Cross out or count back this many.16 - 7
- Write the answer. This is how many are left.9
Check. Add back: 9 + 7 = 16. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.17
- Take away 4. Cross out or count back this many.17 - 4
- Write the answer. This is how many are left.13
Check. Add back: 13 + 4 = 17. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.18
- Take away 3. Cross out or count back this many.18 - 3
- Write the answer. This is how many are left.15
Check. Add back: 15 + 3 = 18. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.15
- Take away 2. Cross out or count back this many.15 - 2
- Write the answer. This is how many are left.13
Check. Add back: 13 + 2 = 15. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.15
- Take away 9. Cross out or count back this many.15 - 9
- Write the answer. This is how many are left.6
Check. Add back: 6 + 9 = 15. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.11
- Take away 4. Cross out or count back this many.11 - 4
- Write the answer. This is how many are left.7
Check. Add back: 7 + 4 = 11. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.17
- Take away 9. Cross out or count back this many.17 - 9
- Write the answer. This is how many are left.8
Check. Add back: 8 + 9 = 17. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.16
- Take away 8. Cross out or count back this many.16 - 8
- Write the answer. This is how many are left.8
Check. Add back: 8 + 8 = 16. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.20
- Take away 2. Cross out or count back this many.20 - 2
- Write the answer. This is how many are left.18
Check. Add back: 18 + 2 = 20. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.11
- Take away 8. Cross out or count back this many.11 - 8
- Write the answer. This is how many are left.3
Check. Add back: 3 + 8 = 11. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.18
- Take away 4. Cross out or count back this many.18 - 4
- Write the answer. This is how many are left.14
Check. Add back: 14 + 4 = 18. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.20
- Take away 4. Cross out or count back this many.20 - 4
- Write the answer. This is how many are left.16
Check. Add back: 16 + 4 = 20. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.15
- Take away 4. Cross out or count back this many.15 - 4
- Write the answer. This is how many are left.11
Check. Add back: 11 + 4 = 15. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.12
- Take away 7. Cross out or count back this many.12 - 7
- Write the answer. This is how many are left.5
Check. Add back: 5 + 7 = 12. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.14
- Take away 5. Cross out or count back this many.14 - 5
- Write the answer. This is how many are left.9
Check. Add back: 9 + 5 = 14. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.20
- Take away 5. Cross out or count back this many.20 - 5
- Write the answer. This is how many are left.15
Check. Add back: 15 + 5 = 20. The answer is right.
Watch out. Count back from the first number, not up from the second.
Number sentences and checking
A number sentence is a sum with the answer, like 7 + 5 = 12.
To check an answer, do the inverse (the opposite). Add undoes take away. Take away undoes add.
Key ideas
- Write the start, the sign, the number, then the answer.
- Use + for more and − for take away.
- Check by doing the opposite: 12 − 5 = 7 is right because 7 + 5 = 12.
Method. Use add for more. Write the start, the sign, the number added and the answer.
- Write the start. Sam starts with 7 cards.7
- Write the sign. More means add.7 +
- Write the rest and the answer. He gets 4 more, so the total is 11.7 + 4 = 11
Check. Check: 11 − 4 = 7. It is right.
Watch out. The equals sign shows the total after the sign.
Method. Do the opposite. Add the number taken away to the answer.
- Look at the subtraction. 13 minus 4 is 8.13 − 4 = 8
- Do the inverse. Add 4 to 8.8 + 4 = 12
- Compare with the start. We needed 13, not 12.12 is not 13
- Write the answer. No
Check. The right answer is 13 − 4 = 9, since 9 + 4 = 13.
Watch out. If the inverse does not give the start, the answer is wrong.
Method. Use take away for fewer. Write the start, the sign, the number taken away and the answer.
- Write the start. There are 15 bees.15
- Write the sign. Fly away means take away.15 −
- Write the rest and the answer. Six fly away, so 9 are left.15 − 6 = 9
Check. Check: 9 + 6 = 15. It is right.
Watch out. Use a minus sign for take away.
Watch out
Watch out. Put the numbers in the right order. 13 − 4 is not the same as 4 − 13.
Exam tip
Grown-up tip. Ask your child to say the story, then write the sum. Check together: “If we add back, do we get the start?”
Exercise 9D Number sentences and checking
Non-calculatorMethod. Use add for more. Write the start, the sign, the number added and the answer.
- Write the start. Amira starts with 12.12
- Write the sign. More means add, so use a plus sign.12 +
- Write the rest and the answer. 5 more are found.12 + 5 = 17
- Check. 12 + 5 = 17
Check. Check with a subtraction: 17 − 5 = 12. ✓
Watch out. Write the sign, then the total after the equals sign.
Method. Use take away for fewer. Write the start, the sign, the number taken away and the answer.
- Write the start. There are 15 bees.15
- Write the sign. Fly away means take away, so use a minus sign.15 −
- Write the rest and the answer. 4 fly away.15 − 4 = 11
- Check. 15 − 4 = 11
Check. Check with addition: 11 + 4 = 15. ✓
Watch out. The minus sign is for taking away. The equals sign shows the answer.
Method. Use add for more. Write the start, the sign, the number added and the answer.
- Write the start. Priya starts with 12.12
- Write the sign. More means add, so use a plus sign.12 +
- Write the rest and the answer. 2 more are found.12 + 2 = 14
- Check. 12 + 2 = 14
Check. Check with a subtraction: 14 − 2 = 12. ✓
Watch out. Write the sign, then the total after the equals sign.
Method. Use take away for fewer. Write the start, the sign, the number taken away and the answer.
- Write the start. There are 8 bees.8
- Write the sign. Fly away means take away, so use a minus sign.8 −
- Write the rest and the answer. 6 fly away.8 − 6 = 2
- Check. 8 − 6 = 2
Check. Check with addition: 2 + 6 = 8. ✓
Watch out. The minus sign is for taking away. The equals sign shows the answer.
Method. Use add for more. Write the start, the sign, the number added and the answer.
- Write the start. Zainab starts with 12.12
- Write the sign. More means add, so use a plus sign.12 +
- Write the rest and the answer. 4 more are found.12 + 4 = 16
- Check. 12 + 4 = 16
Check. Check with a subtraction: 16 − 4 = 12. ✓
Watch out. Write the sign, then the total after the equals sign.
Method. Use take away for fewer. Write the start, the sign, the number taken away and the answer.
- Write the start. There are 10 bees.10
- Write the sign. Fly away means take away, so use a minus sign.10 −
- Write the rest and the answer. 7 fly away.10 − 7 = 3
- Check. 10 − 7 = 3
Check. Check with addition: 3 + 7 = 10. ✓
Watch out. The minus sign is for taking away. The equals sign shows the answer.
Method. Use add for more. Write the start, the sign, the number added and the answer.
- Write the start. Mei starts with 14.14
- Write the sign. More means add, so use a plus sign.14 +
- Write the rest and the answer. 2 more are found.14 + 2 = 16
- Check. 14 + 2 = 16
Check. Check with a subtraction: 16 − 2 = 14. ✓
Watch out. Write the sign, then the total after the equals sign.
Method. Use take away for fewer. Write the start, the sign, the number taken away and the answer.
- Write the start. There are 16 bees.16
- Write the sign. Fly away means take away, so use a minus sign.16 −
- Write the rest and the answer. 14 fly away.16 − 14 = 2
- Check. 16 − 14 = 2
Check. Check with addition: 2 + 14 = 16. ✓
Watch out. The minus sign is for taking away. The equals sign shows the answer.
Method. Use the inverse: take away one of the parts from the answer. Do you get the other part?
- Write the sum. 9 + 7 = 15.9 + 7 = 15
- Do the inverse. Take 7 away from 15.15 - 7 = 8
- Compare with the start. We started with 9.8 is not 9
- Write the answer. No
Check. The correct answer is 16. ✓
Watch out. If the inverse does not give you the start, the sum is wrong.
Method. Use the inverse: add back the number taken away. Do you get the start?
- Write the subtraction. 17 − 8 = 9.17 − 8 = 9
- Do the inverse. Add 8 to 9.9 + 8 = 17
- Compare with the start. We started with 17.17 is the same as 17
- Write the answer. Yes
Check. 9 is the answer, so the sum is right. ✓
Watch out. Add back to check a subtraction.
Method. Use the inverse: take away one of the parts from the answer. Do you get the other part?
- Write the sum. 9 + 4 = 13.9 + 4 = 13
- Do the inverse. Take 4 away from 13.13 - 4 = 9
- Compare with the start. We started with 9.9 is the same as 9
- Write the answer. Yes
Check. 13 is the answer, so the sum is right. ✓
Watch out. If the inverse does not give you the start, the sum is wrong.
Method. Use the inverse: add back the number taken away. Do you get the start?
- Write the subtraction. 16 − 5 = 11.16 − 5 = 11
- Do the inverse. Add 5 to 11.11 + 5 = 16
- Compare with the start. We started with 16.16 is the same as 16
- Write the answer. Yes
Check. 11 is the answer, so the sum is right. ✓
Watch out. Add back to check a subtraction.
Method. Use the inverse: take away one of the parts from the answer. Do you get the other part?
- Write the sum. 7 + 4 = 11.7 + 4 = 11
- Do the inverse. Take 4 away from 11.11 - 4 = 7
- Compare with the start. We started with 7.7 is the same as 7
- Write the answer. Yes
Check. 11 is the answer, so the sum is right. ✓
Watch out. If the inverse does not give you the start, the sum is wrong.
Method. Use the inverse: add back the number taken away. Do you get the start?
- Write the subtraction. 13 − 6 = 7.13 − 6 = 7
- Do the inverse. Add 6 to 7.7 + 6 = 13
- Compare with the start. We started with 13.13 is the same as 13
- Write the answer. Yes
Check. 7 is the answer, so the sum is right. ✓
Watch out. Add back to check a subtraction.
Method. Use the inverse: take away one of the parts from the answer. Do you get the other part?
- Write the sum. 13 + 7 = 20.13 + 7 = 20
- Do the inverse. Take 7 away from 20.20 - 7 = 13
- Compare with the start. We started with 13.13 is the same as 13
- Write the answer. Yes
Check. 20 is the answer, so the sum is right. ✓
Watch out. If the inverse does not give you the start, the sum is wrong.
Method. Use the inverse: add back the number taken away. Do you get the start?
- Write the subtraction. 14 − 9 = 6.14 − 9 = 6
- Do the inverse. Add 9 to 6.6 + 9 = 15
- Compare with the start. We started with 14.15 is not 14
- Write the answer. No
Check. The correct answer is 5. ✓
Watch out. Add back to check a subtraction.
Chapter summary
| Skill | Method |
|---|---|
| Add or take away | More means add. Lost or given away means take away |
| Adding to 20 | Start at the bigger number and count on |
| Taking away from 20 | Start at the number and count back |
| Number sentences | Start, sign, number, answer. Check with the inverse |
Can you…?
- I can choose add or take away from a story
- I can add two numbers to make a total up to 20
- I can take away from a number up to 20
- I can write a number sentence for a story
- I can check an answer by doing the inverse
Key terms
- number story
- a short story with numbers that tells you to add or take away
- number sentence
- a sum with numbers, a sign and an answer
- inverse
- the opposite operation: add undoes take away, and take away undoes add
Exercise 9Z Check-up
Non-calculatorMethod. Read the story. Does the number get bigger or smaller?
- Find the start. Amira starts with 13.13
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Noah starts with 16.16
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Priya starts with 4.4
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.9
- Count on 4 more. We add 4 to 9.9 + 4
- Write the answer. 13
Check. Count on from the other number too. You get 13 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.8
- Count on 2 more. We add 2 to 8.8 + 2
- Write the answer. 10
Check. Count on from the other number too. You get 10 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.11
- Count on 6 more. We add 6 to 11.11 + 6
- Write the answer. 17
Check. Count on from the other number too. You get 17 both ways.
Watch out. Count on, do not start again from one.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.13
- Take away 4. Cross out or count back this many.13 - 4
- Write the answer. This is how many are left.9
Check. Add back: 9 + 4 = 13. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.18
- Take away 2. Cross out or count back this many.18 - 2
- Write the answer. This is how many are left.16
Check. Add back: 16 + 2 = 18. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Use add for more. Write the start, the sign, the number added and the answer.
- Write the start. Amira starts with 12.12
- Write the sign. More means add, so use a plus sign.12 +
- Write the rest and the answer. 6 more are found.12 + 6 = 18
- Check. 12 + 6 = 18
Check. Check with a subtraction: 18 − 6 = 12. ✓
Watch out. Write the sign, then the total after the equals sign.
Method. Use take away for fewer. Write the start, the sign, the number taken away and the answer.
- Write the start. There are 18 bees.18
- Write the sign. Fly away means take away, so use a minus sign.18 −
- Write the rest and the answer. 9 fly away.18 − 9 = 9
- Check. 18 − 9 = 9
Check. Check with addition: 9 + 9 = 18. ✓
Watch out. The minus sign is for taking away. The equals sign shows the answer.
Total 18 marks. Allow about 18 minutes.
Exercise 9X Practice test questions
Non-calculatorMethod. Read the story. Does the number get bigger or smaller?
- Find the start. Amira starts with 12.12
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Noah starts with 7.7
- Decide what happens. Some go, so the number gets smaller.the story changes the number
- Write the word. take away
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Read the story. Does the number get bigger or smaller?
- Find the start. Priya starts with 6.6
- Decide what happens. More are added to the start.the story changes the number
- Write the word. add
Check. Check: the story has a number that changes. Read it again to be sure.
Watch out. More or gets means add. Some go or lose means take away.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.14
- Count on 4 more. We add 4 to 14.14 + 4
- Write the answer. 18
Check. Count on from the other number too. You get 18 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.12
- Count on 2 more. We add 2 to 12.12 + 2
- Write the answer. 14
Check. Count on from the other number too. You get 14 both ways.
Watch out. Count on, do not start again from one.
Method. Put the two groups together. Start at the bigger number and count on.
- Start at the bigger number. It is quicker to count on from the bigger one.11
- Count on 2 more. We add 2 to 11.11 + 2
- Write the answer. 13
Check. Count on from the other number too. You get 13 both ways.
Watch out. Count on, do not start again from one.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.20
- Take away 5. Cross out or count back this many.20 - 5
- Write the answer. This is how many are left.15
Check. Add back: 15 + 5 = 20. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Take away the second number from the first. Count back to check.
- Start with the first number. It is the number of things we begin with.18
- Take away 8. Cross out or count back this many.18 - 8
- Write the answer. This is how many are left.10
Check. Add back: 10 + 8 = 18. The answer is right.
Watch out. Count back from the first number, not up from the second.
Method. Use add for more. Write the start, the sign, the number added and the answer.
- Write the start. Amira starts with 9.9
- Write the sign. More means add, so use a plus sign.9 +
- Write the rest and the answer. 9 more are found.9 + 9 = 18
- Check. 9 + 9 = 18
Check. Check with a subtraction: 18 − 9 = 9. ✓
Watch out. Write the sign, then the total after the equals sign.
Method. Use take away for fewer. Write the start, the sign, the number taken away and the answer.
- Write the start. There are 19 bees.19
- Write the sign. Fly away means take away, so use a minus sign.19 −
- Write the rest and the answer. 12 fly away.19 − 12 = 7
- Check. 19 − 12 = 7
Check. Check with addition: 7 + 12 = 19. ✓
Watch out. The minus sign is for taking away. The equals sign shows the answer.