Step-by-step Maths Level 2 Adding and subtracting within 100: check-up and practice test questions

Method. Take away the tens, then take away the ones. Put the two answers together.

1. Take away the tens: 8 tens - 3 tens. We take the tens from the tens.
   8 - 3 = 5 tens, which is 50
2. Take away the ones: 9 - 7. We take the ones from the ones.
   9 - 7 = 2
3. Put them together: 50 + 2. The tens and the ones make the answer.
   50 + 2 = 52
4. Write the answer.
   52

Check. Add back: 52 + 37 = 89. It is right.

Watch out. Take the ones from the ones and the tens from the tens. Do not take the ones from the tens.

Method. Write the numbers in columns with tens under tens and ones under ones. Work from the ones.

1. Write the numbers in columns. The tens go in one column and the ones in another.
   9 5 and 8 5
2. Take away the ones. Work out the ones first.
   5 - 5 = 0
3. Take away the tens. Then work out the tens.
   9 - 8 = 1
4. Write the answer. Read the tens, then the ones.
   10

Check. Check by adding back: 10 + 85 = 95.

Watch out. Start with the ones column. Keep each digit in its column.

Method. Add the tens, then add the ones. Put the two answers together.

1. Add the tens: 7 tens + 1 tens. Each ten is worth ten.
   7 + 1 = 8 tens, which is 80
2. Add the ones: 2 + 2. The ones are added separately.
   2 + 2 = 4
3. Put them together: 80 + 4. The tens and ones make the total.
   80 + 4 = 84
4. Write the answer.
   84

Check. Count on from 72: you reach 84.

Watch out. Add the tens to the tens and the ones to the ones. Do not add the ones digit to the tens.

Method. Add the tens together. The ones stay the same.

1. Find the tens of 10. 10 is 1 tens.
   10 = 1 tens
2. Add the tens. 8 tens + 1 tens = 9 tens.
   8 + 1 = 9
3. Keep the ones. The ones are still 6.
   9 tens and 6 ones
4. Write the answer.
   96

Check. 86 + 10 goes up by 1 tens. The answer is 96.

Watch out. Adding a multiple of 10 changes only the tens digit.

Method. Add the tens together. The ones stay the same.

1. Find the tens of 20. 20 is 2 tens.
   20 = 2 tens
2. Add the tens. 4 tens + 2 tens = 6 tens.
   4 + 2 = 6
3. Keep the ones. The ones are still 9.
   6 tens and 9 ones
4. Write the answer.
   69

Check. 49 + 20 goes up by 2 tens. The answer is 69.

Watch out. Adding a multiple of 10 changes only the tens digit.

Method. Split the 2-digit number into tens and ones. Add the ones, then put the tens back.

1. Split 61 into 60 and 1. The tens and the ones are kept apart.
   61 = 60 + 1
2. Add the ones: 1 + 2. 1 + 2 = 3 is less than 10, so no tens change.
   1 + 2 = 3
3. Put the tens back: 60 + 3. Add the tens and the ones together.
   60 + 3 = 63
4. Write the answer.
   63

Check. Count on 2 from 61: you reach 63.

Watch out. Only the ones change when you add a 1-digit number and the ones do not go past 9.

Method. Add the tens, then add the ones. Put the two answers together.

1. Add the tens: 5 tens + 4 tens. Each ten is worth ten.
   5 + 4 = 9 tens, which is 90
2. Add the ones: 2 + 3. The ones are added separately.
   2 + 3 = 5
3. Put them together: 90 + 5. The tens and ones make the total.
   90 + 5 = 95
4. Write the answer.
   95

Check. Count on from 52: you reach 95.

Watch out. Add the tens to the tens and the ones to the ones. Do not add the ones digit to the tens.

Method. Write the numbers in columns with tens under tens and ones under ones. Work from the ones.

1. Write the numbers in columns. The tens go in one column and the ones in another.
   6 8 and 1 1
2. Add the ones. Work out the ones first.
   8 + 1 = 9
3. Add the tens. Then work out the tens.
   6 + 1 = 7
4. Write the answer. Read the tens, then the ones.
   79

Check. Check by taking 11 away: 79 - 11 = 68.

Watch out. Start with the ones column. Keep each digit in its column.

Method. Split the 2-digit number into tens and ones. Add the ones, then put the tens back.

1. Split 26 into 20 and 6. The tens and the ones are kept apart.
   26 = 20 + 6
2. Add the ones: 6 + 2. 6 + 2 = 8 is less than 10, so no tens change.
   6 + 2 = 8
3. Put the tens back: 20 + 8. Add the tens and the ones together.
   20 + 8 = 28
4. Write the answer.
   28

Check. Count on 2 from 26: you reach 28.

Watch out. Only the ones change when you add a 1-digit number and the ones do not go past 9.

Method. Add the tens together. The ones stay the same.

1. Find the tens of 70. 70 is 7 tens.
   70 = 7 tens
2. Add the tens. 1 tens + 7 tens = 8 tens.
   1 + 7 = 8
3. Keep the ones. The ones are still 3.
   8 tens and 3 ones
4. Write the answer.
   83

Check. 13 + 70 goes up by 7 tens. The answer is 83.

Watch out. Adding a multiple of 10 changes only the tens digit.

Method. Split the 2-digit number into tens and ones. Add the ones, then put the tens back.

1. Split 62 into 60 and 2. The tens and the ones are kept apart.
   62 = 60 + 2
2. Add the ones: 2 + 6. 2 + 6 = 8 is less than 10, so no tens change.
   2 + 6 = 8
3. Put the tens back: 60 + 8. Add the tens and the ones together.
   60 + 8 = 68
4. Write the answer.
   68

Check. Count on 6 from 62: you reach 68.

Watch out. Only the ones change when you add a 1-digit number and the ones do not go past 9.

Method. Write the numbers in columns with tens under tens and ones under ones. Work from the ones.

1. Write the numbers in columns. The tens go in one column and the ones in another.
   5 3 and 3 6
2. Add the ones. Work out the ones first.
   3 + 6 = 9
3. Add the tens. Then work out the tens.
   5 + 3 = 8
4. Write the answer. Read the tens, then the ones.
   89

Check. Check by taking 36 away: 89 - 36 = 53.

Watch out. Start with the ones column. Keep each digit in its column.

Method. Add the tens together. The ones stay the same.

1. Find the tens of 30. 30 is 3 tens.
   30 = 3 tens
2. Add the tens. 4 tens + 3 tens = 7 tens.
   4 + 3 = 7
3. Keep the ones. The ones are still 7.
   7 tens and 7 ones
4. Write the answer.
   77

Check. 47 + 30 goes up by 3 tens. The answer is 77.

Watch out. Adding a multiple of 10 changes only the tens digit.

Method. Write the numbers in columns with tens under tens and ones under ones. Work from the ones.

1. Write the numbers in columns. The tens go in one column and the ones in another.
   4 9 and 1 0
2. Take away the ones. Work out the ones first.
   9 - 0 = 9
3. Take away the tens. Then work out the tens.
   4 - 1 = 3
4. Write the answer. Read the tens, then the ones.
   39

Check. Check by adding back: 39 + 10 = 49.

Watch out. Start with the ones column. Keep each digit in its column.

Method. Add the tens, then add the ones. Put the two answers together.

1. Add the tens: 2 tens + 4 tens. Each ten is worth ten.
   2 + 4 = 6 tens, which is 60
2. Add the ones: 6 + 1. The ones are added separately.
   6 + 1 = 7
3. Put them together: 60 + 7. The tens and ones make the total.
   60 + 7 = 67
4. Write the answer.
   67

Check. Count on from 26: you reach 67.

Watch out. Add the tens to the tens and the ones to the ones. Do not add the ones digit to the tens.

Method. Take away the tens, then take away the ones. Put the two answers together.

1. Take away the tens: 6 tens - 1 tens. We take the tens from the tens.
   6 - 1 = 5 tens, which is 50
2. Take away the ones: 6 - 3. We take the ones from the ones.
   6 - 3 = 3
3. Put them together: 50 + 3. The tens and the ones make the answer.
   50 + 3 = 53
4. Write the answer.
   53

Check. Add back: 53 + 13 = 66. It is right.

Watch out. Take the ones from the ones and the tens from the tens. Do not take the ones from the tens.

Method. Split the 2-digit number into tens and ones. Add the ones, then put the tens back.

1. Split 48 into 40 and 8. The tens and the ones are kept apart.
   48 = 40 + 8
2. Add the ones: 8 + 1. 8 + 1 = 9 is less than 10, so no tens change.
   8 + 1 = 9
3. Put the tens back: 40 + 9. Add the tens and the ones together.
   40 + 9 = 49
4. Write the answer.
   49

Check. Count on 1 from 48: you reach 49.

Watch out. Only the ones change when you add a 1-digit number and the ones do not go past 9.

Method. Write the numbers in columns with tens under tens and ones under ones. Work from the ones.

1. Write the numbers in columns. The tens go in one column and the ones in another.
   3 7 and 2 5
2. Take away the ones. Work out the ones first.
   7 - 5 = 2
3. Take away the tens. Then work out the tens.
   3 - 2 = 1
4. Write the answer. Read the tens, then the ones.
   12

Check. Check by adding back: 12 + 25 = 37.

Watch out. Start with the ones column. Keep each digit in its column.

Method. Add the tens, then add the ones. Put the two answers together.

1. Add the tens: 2 tens + 6 tens. Each ten is worth ten.
   2 + 6 = 8 tens, which is 80
2. Add the ones: 8 + 1. The ones are added separately.
   8 + 1 = 9
3. Put them together: 80 + 9. The tens and ones make the total.
   80 + 9 = 89
4. Write the answer.
   89

Check. Count on from 28: you reach 89.

Watch out. Add the tens to the tens and the ones to the ones. Do not add the ones digit to the tens.

Method. Take away the tens, then take away the ones. Put the two answers together.

1. Take away the tens: 7 tens - 4 tens. We take the tens from the tens.
   7 - 4 = 3 tens, which is 30
2. Take away the ones: 8 - 0. We take the ones from the ones.
   8 - 0 = 8
3. Put them together: 30 + 8. The tens and the ones make the answer.
   30 + 8 = 38
4. Write the answer.
   38

Check. Add back: 38 + 40 = 78. It is right.

Watch out. Take the ones from the ones and the tens from the tens. Do not take the ones from the tens.