Year 2: Adding and taking away tens
Part of the Year 2 adding and subtracting chapter. Chapter overview · whole chapter on one page
Adding and taking away tens
Adding or taking away tens changes only the tens digit.
Look at 34 + 30. The ones stay 4. The tens are 3 + 3 = 6 tens. So 34 + 30 = 64.
On a 100 square, adding 10 goes down one row. Taking away 10 goes up one row.
Key ideas
- Adding or taking away tens changes only the tens digit.
- Adding 10 moves down one row on the 100 square.
- Taking away 10 moves up one row.
- The ones digit stays the same.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 34 has 3 tens. We add 3 tens.3 tens + 3 tens
- Work out the new tens. 3 + 3 = 6, so there are 6 tens.6 tens = 60
- Keep the ones the same. The ones digit is 4 and it does not change.4 ones stay
- Put the parts together. 60 and 4 make 64.60 + 4 = 64
Check. 34 + 30 = 64. Count in tens to check. ✓
Watch out. Do not change the ones digit. 34 becomes 64, not 35.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 58 has 5 tens. We take away 2 tens.5 tens − 2 tens
- Work out the new tens. 5 − 2 = 3, so there are 3 tens.3 tens = 30
- Keep the ones the same. The ones digit is 8 and it does not change.8 ones stay
- Put the parts together. 30 and 8 make 38.30 + 8 = 38
Check. 58 − 20 = 38. Count in tens to check. ✓
Watch out. Do not change the ones digit. 58 becomes 38, not 57.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 45 has 4 tens. We add 4 tens.4 tens + 4 tens
- Work out the new tens. 4 + 4 = 8, so there are 8 tens.8 tens = 80
- Keep the ones the same. The ones digit is 5 and it does not change.5 ones stay
- Put the parts together. 80 and 5 make 85.80 + 5 = 85
Check. 45 + 40 = 85. Count in tens to check. ✓
Watch out. Do not change the ones digit. 45 becomes 85, not 46.
Watch out
Watch out: 34 + 30 is 64, not 37. Only the tens change.
Exam tip
Grown-up tip. Use bundles of ten pasta or straws. Ask: “Add 3 bundles to 4 loose pieces. How many bundles now? How many loose pieces?”
Exercise 2C Adding and taking away tens
Non-calculatorKey words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 36 has 3 tens. We add 2 tens.3 tens + 2 tens
- Work out the new tens. 3 + 2 = 5, so there are 5 tens.5 tens = 50
- Keep the ones the same. The ones digit is 6 and it does not change.6 ones stay
- Put the parts together. 50 and 6 make 56.50 + 6 = 56
Check. 36 + 20 = 56. Count in tens to check. ✓
Watch out. Do not change the ones digit. 36 becomes 56, not 37.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 58 has 5 tens. We take away 3 tens.5 tens − 3 tens
- Work out the new tens. 5 − 3 = 2, so there are 2 tens.2 tens = 20
- Keep the ones the same. The ones digit is 8 and it does not change.8 ones stay
- Put the parts together. 20 and 8 make 28.20 + 8 = 28
Check. 58 − 30 = 28. Count in tens to check. ✓
Watch out. Do not change the ones digit. 58 becomes 28, not 57.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 45 has 4 tens. We add 4 tens.4 tens + 4 tens
- Work out the new tens. 4 + 4 = 8, so there are 8 tens.8 tens = 80
- Keep the ones the same. The ones digit is 5 and it does not change.5 ones stay
- Put the parts together. 80 and 5 make 85.80 + 5 = 85
Check. 45 + 40 = 85. Count in tens to check. ✓
Watch out. Do not change the ones digit. 45 becomes 85, not 46.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 26 has 2 tens. We add 5 tens.2 tens + 5 tens
- Work out the new tens. 2 + 5 = 7, so there are 7 tens.7 tens = 70
- Keep the ones the same. The ones digit is 6 and it does not change.6 ones stay
- Put the parts together. 70 and 6 make 76.70 + 6 = 76
Check. 26 + 50 = 76. Count in tens to check. ✓
Watch out. Do not change the ones digit. 26 becomes 76, not 27.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 90 has 9 tens. We take away 6 tens.9 tens − 6 tens
- Work out the new tens. 9 − 6 = 3, so there are 3 tens.3 tens = 30
- Keep the ones the same. The ones digit is 0 and it does not change.0 ones stay
- Put the parts together. 30 and 0 make 30.30 + 0 = 30
Check. 90 − 60 = 30. Count in tens to check. ✓
Watch out. Do not change the ones digit. 90 becomes 30, not 89.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 23 has 2 tens. We add 1 ten.2 tens + 1 tens
- Work out the new tens. 2 + 1 = 3, so there are 3 tens.3 tens = 30
- Keep the ones the same. The ones digit is 3 and it does not change.3 ones stay
- Put the parts together. 30 and 3 make 33.30 + 3 = 33
Check. 23 + 10 = 33. Count in tens to check. ✓
Watch out. Do not change the ones digit. 23 becomes 33, not 24.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 47 has 4 tens. We take away 2 tens.4 tens − 2 tens
- Work out the new tens. 4 − 2 = 2, so there are 2 tens.2 tens = 20
- Keep the ones the same. The ones digit is 7 and it does not change.7 ones stay
- Put the parts together. 20 and 7 make 27.20 + 7 = 27
Check. 47 − 20 = 27. Count in tens to check. ✓
Watch out. Do not change the ones digit. 47 becomes 27, not 46.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 62 has 6 tens. We add 3 tens.6 tens + 3 tens
- Work out the new tens. 6 + 3 = 9, so there are 9 tens.9 tens = 90
- Keep the ones the same. The ones digit is 2 and it does not change.2 ones stay
- Put the parts together. 90 and 2 make 92.90 + 2 = 92
Check. 62 + 30 = 92. Count in tens to check. ✓
Watch out. Do not change the ones digit. 62 becomes 92, not 63.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 19 has 1 ten. We add 6 tens.1 tens + 6 tens
- Work out the new tens. 1 + 6 = 7, so there are 7 tens.7 tens = 70
- Keep the ones the same. The ones digit is 9 and it does not change.9 ones stay
- Put the parts together. 70 and 9 make 79.70 + 9 = 79
Check. 19 + 60 = 79. Count in tens to check. ✓
Watch out. Do not change the ones digit. 19 becomes 79, not 20.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 84 has 8 tens. We take away 4 tens.8 tens − 4 tens
- Work out the new tens. 8 − 4 = 4, so there are 4 tens.4 tens = 40
- Keep the ones the same. The ones digit is 4 and it does not change.4 ones stay
- Put the parts together. 40 and 4 make 44.40 + 4 = 44
Check. 84 − 40 = 44. Count in tens to check. ✓
Watch out. Do not change the ones digit. 84 becomes 44, not 83.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 31 has 3 tens. We add 4 tens.3 tens + 4 tens
- Work out the new tens. 3 + 4 = 7, so there are 7 tens.7 tens = 70
- Keep the ones the same. The ones digit is 1 and it does not change.1 ones stay
- Put the parts together. 70 and 1 make 71.70 + 1 = 71
Check. 31 + 40 = 71. Count in tens to check. ✓
Watch out. Do not change the ones digit. 31 becomes 71, not 32.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 42 has 4 tens. We add 3 tens.4 tens + 3 tens
- Work out the new tens. 4 + 3 = 7, so there are 7 tens.7 tens = 70
- Keep the ones the same. The ones digit is 2 and it does not change.2 ones stay
- Put the parts together. 70 and 2 make 72.70 + 2 = 72
Check. 42 + 30 = 72. Count in tens to check. ✓
Watch out. Do not change the ones digit. 42 becomes 72, not 43.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 83 has 8 tens. We take away 2 tens.8 tens − 2 tens
- Work out the new tens. 8 − 2 = 6, so there are 6 tens.6 tens = 60
- Keep the ones the same. The ones digit is 3 and it does not change.3 ones stay
- Put the parts together. 60 and 3 make 63.60 + 3 = 63
Check. 83 − 20 = 63. Count in tens to check. ✓
Watch out. Do not change the ones digit. 83 becomes 63, not 82.
Key words. Adding tens means adding groups of ten.
Method. Only the tens change. The ones stay the same.
- Look at the tens. 64 has 6 tens. We take away 4 tens.6 tens − 4 tens
- Work out the new tens. 6 − 4 = 2, so there are 2 tens.2 tens = 20
- Keep the ones the same. The ones digit is 4 and it does not change.4 ones stay
- Put the parts together. 20 and 4 make 24.20 + 4 = 24
Check. 64 − 40 = 24. Count in tens to check. ✓
Watch out. Do not change the ones digit. 64 becomes 24, not 63.
Method. Work out the sum or difference, then compare it with what was said.
- Work out 36 + 20. Use a method that you know.36 + 20 = 56
- Compare with the claim. The claim says 46, but the answer is 56.No. 36 + 20 = 56
Check. Take 20 away from 56. You get 36. ✓
Watch out. Check the tens first, then the ones. A carry or an exchange is easy to forget.
Method. Work out each sum first. Then compare them.
- Work out 45 + 30. 4 tens and 3 tens make 7 tens.45 + 30 = 75
- Work out 60 + 10. 6 tens and 1 ten make 7 tens.60 + 10 = 70
- Compare the answers. 75 is more than 70.45 + 30
Check. 75 is 5 more than 70, so 45 + 30 is the bigger sum. ✓
Watch out. Look at the tens first, then the ones.