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Step-by-step practice: Maths · Level 2Chapter 5 · Adding within 20
Level 2 · Chapter 5

Adding within 20

By the end of this chapter you will be able to

  • Count on to add
  • Make 10 to help with adding
  • Add a 1-digit number to a 2-digit number
  • Know that adding zero does not change a number
  • Write and complete number sentences

You should already know

  • Number bonds to 10 (Level 1)
  • Number bonds to 20 (Chapter 4)
  • Tens and ones (Chapter 2)

Where this leads

  • Taking away within 20 (Chapter 6)
  • Adding and subtracting within 100 (Chapter 7)

Step-by-step practice: maths (Level 2). Small steps, repeated until fluent. Content: Add two numbers with a total up to 20 by counting on from the bigger number, Make 10 first to add numbers that go past 10, Add a 1-digit number to a 2-digit number up to 20, Add zero, and see that adding zero does not change a number, Write number sentences with + and =, and find missing numbers.

Exercise P  Do you remember?

Non-calculator
1
FWork out 2 + 6.
56789
2
FWork out 9 + 3. Make 10 first.
3
F12 + 0 = ?
4
FWrite a number sentence for 4 and 5 together.
5
FWrite the missing number: 7 + ? = 15
5.1

Counting on to add

Level 2
Add two numbers with a total up to 20 by counting on
Video lesson: Counting on to addComing soon

To add, start at the bigger number. Then count on the smaller number.

Starting at the bigger number is quicker. For 5 + 8, start at 8 and count on 5.

789101112131415
Start at 8 and count on 5. You reach 13.

Key ideas

  • Start at the bigger number.
  • Count on the smaller number.
  • The total is the last number you say.
Worked example 5.1.1
Work out 8 + 5.

Method. Start with the bigger number and count on the smaller number.

  1. Start at the bigger number, 8. It is quicker to count on from the bigger number.
    8
  2. Count on 5 more. Say 5 numbers after 8.
    8 + 5 = 13
  3. Write the answer. This is the last number we said.
    13

Check. Start at 5 and count on 8. You also reach 13.

Watch out. Count on from the bigger number. Do not start again at one.

Worked example 5.1.2
Work out 3 + 9.

Method. Start with the bigger number and count on the smaller number.

  1. Start at the bigger number, 9. It is quicker to count on from the bigger number.
    9
  2. Count on 3 more. Say 3 numbers after 9.
    9 + 3 = 12
  3. Write the answer. This is the last number we said.
    12

Check. Start at 3 and count on 9. You also reach 12.

Watch out. Count on from the bigger number. Do not start again at one.

Worked example 5.1.3
Work out 6 + 7.

Method. Start with the bigger number and count on the smaller number.

  1. Start at the bigger number, 7. It is quicker to count on from the bigger number.
    7
  2. Count on 6 more. Say 6 numbers after 7.
    7 + 6 = 13
  3. Write the answer. This is the last number we said.
    13

Check. Start at 6 and count on 7. You also reach 13.

Watch out. Count on from the bigger number. Do not start again at one.

Watch out

Watch out. Do not start at 1 and count everything. Start at the bigger number.

Exam tip

Grown-up tip. Use two cups of counters. Tip one into the other and count the total from the bigger cup.

Exercise 5A  Practice: counting on to add

Non-calculator
1
FWork out 6 + 6.
5678910111213
2
FWork out 9 + 5.
89101112131415
3
FWork out 1 + 2.
1234
4
FWork out 2 + 9.
89101112
5
FWork out 3 + 5.
456789
6
FWork out 4 + 1.
3456
7
FWork out 8 + 8.
7891011121314151617
8
FWork out 5 + 9.
89101112131415
9
FWork out 4 + 8.
78910111213
10
FWork out 2 + 5.
45678
11
FWork out 7 + 6.
67891011121314
12
FWork out 5 + 1.
4567
13
FWork out 1 + 3.
2345
14
FWork out 3 + 4.
345678
15
FWork out 7 + 8.
78910111213141516
16
FWork out 9 + 7.
891011121314151617
5.2

Making 10 first

Level 2
Make 10 first to add numbers that go past 10
Video lesson: Making 10 firstComing soon

Some sums go past 10. To make them easier, make 10 first.

Split the second number so that the first number reaches 10. Then add what is left.

The first frame has 10 counters. The second frame has 3 more.

Key ideas

  • Make 10 first, then add the rest.
  • Use bonds to 10 to find how many make 10.
  • Adding to 10 is easy.
Worked example 5.2.1
Work out 8 + 5. Make 10 first.

Method. Use the number that makes 10 with the first number. Then add what is left.

  1. Find what 8 needs to make 10. 8 needs 2 more to make 10.
    10 - 8 = 2
  2. Split 5 into 2 and 3. Use 2 to make 10. Then add 3.
    5 = 2 + 3
  3. Add the rest to 10. 8 + 2 = 10, and 10 + 3 = 13.
    10 + 3 = 13
  4. Write the answer.
    13

Check. Count on: 8 + 5 = 13.

Watch out. Making 10 first is easier because 10 is simple to add to.

Worked example 5.2.2
Work out 7 + 6. Make 10 first.

Method. Use the number that makes 10 with the first number. Then add what is left.

  1. Find what 7 needs to make 10. 7 needs 3 more to make 10.
    10 - 7 = 3
  2. Split 6 into 3 and 3. Use 3 to make 10. Then add 3.
    6 = 3 + 3
  3. Add the rest to 10. 7 + 3 = 10, and 10 + 3 = 13.
    10 + 3 = 13
  4. Write the answer.
    13

Check. Count on: 7 + 6 = 13.

Watch out. Making 10 first is easier because 10 is simple to add to.

Worked example 5.2.3
Work out 9 + 4. Make 10 first.

Method. Use the number that makes 10 with the first number. Then add what is left.

  1. Find what 9 needs to make 10. 9 needs 1 more to make 10.
    10 - 9 = 1
  2. Split 4 into 1 and 3. Use 1 to make 10. Then add 3.
    4 = 1 + 3
  3. Add the rest to 10. 9 + 1 = 10, and 10 + 3 = 13.
    10 + 3 = 13
  4. Write the answer.
    13

Check. Count on: 9 + 4 = 13.

Watch out. Making 10 first is easier because 10 is simple to add to.

Watch out

Watch out. When you split the second number, use the right part to make 10. 8 needs 2, not 5.

Exam tip

Grown-up tip. Use a ten frame. Fill it up to ten, then count the counters left over.

Exercise 5B  Practice: making 10 first

Non-calculator
1
FWork out 8 + 5. Make 10 first.
2
FWork out 4 + 8. Make 10 first.
3
FWork out 5 + 7. Make 10 first.
4
FWork out 8 + 6. Make 10 first.
5
FWork out 6 + 9. Make 10 first.
6
FWork out 8 + 4. Make 10 first.
7
FWork out 9 + 4. Make 10 first.
8
FWork out 8 + 7. Make 10 first.
9
FWork out 9 + 6. Make 10 first.
10
FWork out 7 + 7. Make 10 first.
11
FWork out 9 + 8. Make 10 first.
12
FWork out 8 + 8. Make 10 first.
13
FWork out 4 + 9. Make 10 first.
14
FWork out 6 + 8. Make 10 first.
15
FWork out 7 + 6. Make 10 first.
16
FWork out 4 + 7. Make 10 first.
5.3

Adding a 1-digit number to a 2-digit number

Level 2
Add a 1-digit number to a 2-digit number up to 20
Video lesson: Adding a 1-digit number to a 2-digit numberComing soon

A 2-digit number like 14 is 10 and 4. To add 5, add 5 to the ones: 4 + 5 = 9.

Then put the 10 back: 10 + 9 = 19.

Fourteen is one full ten and four more.

Key ideas

  • A 2-digit number has a ten and some ones.
  • Add the 1-digit number to the ones.
  • Put the 10 back on the total.
Worked example 5.3.1
Work out 14 + 5.

Method. Split the 2-digit number into 10 and the ones. Add the ones, then add 10.

  1. Split 14 into 10 and 4. The tens part is 10. The ones part is what is left.
    14 = 10 + 4
  2. Add the ones: 4 + 5. Add the ones part to the number that is added.
    4 + 5 = 9
  3. Add 10 back. Put the 10 back on the total.
    10 + 9 = 19
  4. Write the answer.
    19

Check. Count on 5 from 14: you reach 19.

Watch out. Remember the 10 when you add the ones. 14 + 5 is 19, not 9.

Worked example 5.3.2
Work out 16 + 3.

Method. Split the 2-digit number into 10 and the ones. Add the ones, then add 10.

  1. Split 16 into 10 and 6. The tens part is 10. The ones part is what is left.
    16 = 10 + 6
  2. Add the ones: 6 + 3. Add the ones part to the number that is added.
    6 + 3 = 9
  3. Add 10 back. Put the 10 back on the total.
    10 + 9 = 19
  4. Write the answer.
    19

Check. Count on 3 from 16: you reach 19.

Watch out. Remember the 10 when you add the ones. 14 + 5 is 19, not 9.

Worked example 5.3.3
Work out 12 + 8.

Method. Split the 2-digit number into 10 and the ones. Add the ones, then add 10.

  1. Split 12 into 10 and 2. The tens part is 10. The ones part is what is left.
    12 = 10 + 2
  2. Add the ones: 2 + 8. Add the ones part to the number that is added.
    2 + 8 = 10
  3. Add 10 back. Put the 10 back on the total.
    10 + 10 = 20
  4. Write the answer.
    20

Check. Count on 8 from 12: you reach 20.

Watch out. Remember the 10 when you add the ones. 14 + 5 is 19, not 9.

Watch out

Watch out. 14 + 5 is 19, not 9. Remember the ten.

Exam tip

Grown-up tip. Ask: “How many tens and ones are in 16?” before adding. Then add to the ones.

Exercise 5C  Practice: adding to a 2-digit number

Non-calculator
1
FWork out 11 + 4.
2
FWork out 13 + 6.
3
FWork out 14 + 5.
4
FWork out 10 + 4.
5
FWork out 11 + 9.
6
FWork out 14 + 3.
7
FWork out 17 + 1.
8
FWork out 12 + 6.
9
FWork out 10 + 2.
10
FWork out 15 + 1.
11
FWork out 17 + 2.
12
FWork out 12 + 1.
13
FWork out 10 + 7.
14
FWork out 18 + 2.
15
FWork out 12 + 5.
16
FWork out 16 + 1.
5.4

Adding zero

Level 2
Add zero, and see that adding zero does not change a number
Video lesson: Adding zeroComing soon

Zero means none. When you add zero, you add nothing.

So the number stays the same, whether zero is first or second in the sum.

Key ideas

  • Adding zero does not change a number.
  • 9 + 0 = 9 and 0 + 9 = 9.
  • Zero can go first or second.
Worked example 5.4.1
9 + 0 = ?

Method. Adding zero means we add nothing. The number stays the same.

  1. Look at the number. It is the number we start with.
    9
  2. Add zero. Zero adds no more things.
    9 + 0 = 9
  3. Write the answer. The number does not change.
    9

Check. Take zero away from 9: it is still 9.

Watch out. Adding zero never changes a number, whether zero is first or second.

Worked example 5.4.2
0 + 14 = ?

Method. Adding zero means we add nothing. The number stays the same.

  1. Look at the number. It is the number we start with.
    14
  2. Add zero. Zero adds no more things.
    0 + 14 = 14
  3. Write the answer. The number does not change.
    14

Check. Take zero away from 14: it is still 14.

Watch out. Adding zero never changes a number, whether zero is first or second.

Worked example 5.4.3
17 + 0 = ?

Method. Adding zero means we add nothing. The number stays the same.

  1. Look at the number. It is the number we start with.
    17
  2. Add zero. Zero adds no more things.
    17 + 0 = 17
  3. Write the answer. The number does not change.
    17

Check. Take zero away from 17: it is still 17.

Watch out. Adding zero never changes a number, whether zero is first or second.

Watch out

Watch out. Some children think adding zero makes the number zero. It does not.

Exam tip

Grown-up tip. Ask: “If we have 6 sweets and get none more, how many do we have?”

Exercise 5D  Practice: adding zero

Non-calculator
1
F7 + 0 = ?
2
F18 + 0 = ?
3
F6 + 0 = ?
4
F11 + 0 = ?
5
F13 + 0 = ?
6
F15 + 0 = ?
7
F0 + 4 = ?
8
F2 + 0 = ?
9
F0 + 6 = ?
10
F19 + 0 = ?
11
F0 + 20 = ?
12
F4 + 0 = ?
13
F17 + 0 = ?
14
F20 + 0 = ?
15
F0 + 13 = ?
16
F1 + 0 = ?
5.5

Number sentences

Level 2
Write number sentences with + and =, Find a missing number in a sum
Video lesson: Number sentencesComing soon

A number sentence uses numbers and signs. The plus sign + means add. The equals sign = means the same as.

The sign goes between the parts. The total goes after the equals sign.

Key ideas

  • + means add. = means the same as.
  • The total goes after =.
  • A missing number is a gap to fill in.
Worked example 5.5.1
Write a number sentence for 8 and 7 together.

Method. Write the two parts with a plus sign, then the answer after an equals sign.

  1. Write the parts. Put a plus sign between the two parts.
    8 + 7
  2. Work out the total. The total goes after the equals sign.
    8 + 7 = 15
  3. Write the number sentence.
    8 + 7 = 15

Check. 15 - 7 = 8. The sentence is right.

Watch out. The equals sign is for the total. Do not write the answer before the sign.

Worked example 5.5.2
Write the missing number: 9 + ? = 15

Method. Find the missing part. Ask what goes with the known part to make the total.

  1. Start with 9. It is the part we know.
    9
  2. Count on to 15. Or take the known part away from the total.
    15 - 9 = 6
  3. Write the missing number.
    6

Check. 9 + 6 = 15. It works.

Watch out. Take the known part away from the total to find the missing one.

Worked example 5.5.3
Write the missing number: 5 + ? = 16

Method. Find the missing part. Ask what goes with the known part to make the total.

  1. Start with 5. It is the part we know.
    5
  2. Count on to 16. Or take the known part away from the total.
    16 - 5 = 11
  3. Write the missing number.
    11

Check. 5 + 11 = 16. It works.

Watch out. Take the known part away from the total to find the missing one.

Watch out

Watch out. The answer goes after the equals sign, not before it.

Exam tip

Grown-up tip. Read the sentence out loud: “nine add six makes fifteen.”

Exercise 5E  Practice: number sentences

Non-calculator
1
FWrite the missing number: 6 + ? = 10
2
FWrite the missing number: 11 + ? = 18
3
FWrite a number sentence for 1 and 5 together.
4
FWrite the missing number: 10 + ? = 16
5
FWrite a number sentence for 14 and 2 together.
6
FWrite the missing number: 13 + ? = 19
7
FWrite the missing number: 11 + ? = 14
8
FWrite a number sentence for 5 and 11 together.
9
FWrite a number sentence for 5 and 5 together.
10
FWrite the missing number: 13 + ? = 15
11
FWrite a number sentence for 8 and 12 together.
12
FWrite the missing number: 2 + ? = 10
13
FWrite the missing number: 14 + ? = 20
14
FWrite the missing number: 3 + ? = 17
15
FWrite the missing number: 2 + ? = 5
16
FWrite the missing number: 7 + ? = 18

Chapter summary

SkillMethod
Counting onStart at the bigger number and count on the smaller
Making 10Make 10 first, then add the rest
2-digit plus 1-digitAdd to the ones, then put the 10 back
Adding zeroThe number stays the same
Number sentencesParts with +, total after =

Can you…?

  • I can add two numbers by counting on from the bigger number
  • I can make 10 first to add numbers that go past 10
  • I can add a 1-digit number to a 2-digit number up to 20
  • I know that adding zero does not change a number
  • I can write and complete number sentences

Key terms

add
put numbers together to find the total
total
the answer when numbers are added
number sentence
numbers and signs that show a fact, such as 8 + 7 = 15
make 10
split a number so that one part makes 10 with the first number

Exercise 5Z  Check-up

Non-calculator
1
0 + 4 = ?
2
Work out 10 + 9.
3
15 + 0 = ?
4
Work out 6 + 6. Make 10 first.
5
Work out 13 + 3.
6
5 + 0 = ?
7
Work out 3 + 9. Make 10 first.
8
Work out 12 + 5.
9
Work out 7 + 6.
67891011121314
10
13 + 0 = ?

Total 19 marks. Allow about 19 minutes.

Exercise 5X  Practice test questions

Non-calculator
1
F7 + 0 = ?[1 mark]
2
FWrite a number sentence for 12 and 6 together.[1 mark]
3
FWork out 1 + 5.[1 mark]
4567
4
FWork out 2 + 2.[1 mark]
12345
5
FWrite a number sentence for 1 and 5 together.[2 marks]
6
FWork out 12 + 8.[2 marks]
7
FWork out 14 + 6.[2 marks]
8
FWrite the missing number: 5 + ? = 9[3 marks]
9
FWork out 7 + 7. Make 10 first.[3 marks]
10
FWork out 19 + 1.[3 marks]
← Chapter 4: Number bonds to 20Chapter 6: Taking away within 20 →

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