Year 2: Adding and taking away ones
Part of the Year 2 adding and subtracting chapter. Chapter overview · whole chapter on one page
Adding and taking away ones
A two-digit number has tens and ones. To add or take away ones, only the ones change.
Look at 34 + 5. The tens stay at 3 tens. The ones make 4 + 5 = 9. So 34 + 5 = 39.
Sometimes the ones make 10 or more. Then we make a new ten.
Key ideas
- Add the ones to the ones.
- The tens stay the same unless we make a new ten.
- If the ones make 10 or more, make a new ten.
- Take away the ones, then keep the tens.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 4 ones and 5 ones make 9 ones.4 + 5 = 9
- Keep the tens the same. Adding ones does not change the tens.3 tens stay the same
- Put the parts together. 30 and 9 make 39.30 + 9 = 39
Check. Take 5 away from 39. You get 34. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 8 + 5 = 13. That is 10 or more ones, so make a new ten.8 + 5 = 13
- Make a new ten. 13 ones is 1 ten and 3 ones.13 = 1 ten and 3 ones
- Add the new ten to the tens. 3 tens and 1 more ten make 4 tens.40
- Put the parts together. 40 and 3 make 43.40 + 3 = 43
Check. Take 5 away from 43. You get 38. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. You cannot take 5 from 2, so take 1 ten.2 is less than 5
- Exchange 1 ten for 10 ones. 4 tens becomes 3 tens and 12 ones.2 + 10 = 12
- Take the ones away. 12 − 5 = 712 − 5 = 7
- Put the parts together. 30 and 7 make 37.30 + 7 = 37
Check. Add 5 to 37. You get 42. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Watch out
Watch out: 38 + 5 is 43, not 33. The ones make 13, so we make a new ten.
Exam tip
Grown-up tip. Use 3 bundles of ten pasta and 4 loose pieces. Ask: “Add 5 more single pieces. How many now?” Then ask: “Did we make a new bundle?”
Exercise 2B Adding and taking away ones
Non-calculatorKey words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 3 ones and 4 ones make 7 ones.3 + 4 = 7
- Keep the tens the same. Adding ones does not change the tens.2 tens stay the same
- Put the parts together. 20 and 7 make 27.20 + 7 = 27
Check. Take 4 away from 27. You get 23. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. Take 3 ones away from 6 ones.6 − 3 = 3
- Keep the tens the same. Taking ones away does not change the tens.5 tens stay the same
- Put the parts together. 50 and 3 make 53.50 + 3 = 53
Check. Add 3 to 53. You get 56. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 7 ones and 2 ones make 9 ones.7 + 2 = 9
- Keep the tens the same. Adding ones does not change the tens.3 tens stay the same
- Put the parts together. 30 and 9 make 39.30 + 9 = 39
Check. Take 2 away from 39. You get 37. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 8 + 6 = 14. That is 10 or more ones, so make a new ten.8 + 6 = 14
- Make a new ten. 14 ones is 1 ten and 4 ones.14 = 1 ten and 4 ones
- Add the new ten to the tens. 4 tens and 1 more ten make 5 tens.50
- Put the parts together. 50 and 4 make 54.50 + 4 = 54
Check. Take 6 away from 54. You get 48. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. You cannot take 7 from 5, so take 1 ten.5 is less than 7
- Exchange 1 ten for 10 ones. 6 tens becomes 5 tens and 15 ones.5 + 10 = 15
- Take the ones away. 15 − 7 = 815 − 7 = 8
- Put the parts together. 50 and 8 make 58.50 + 8 = 58
Check. Add 7 to 58. You get 65. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 4 ones and 3 ones make 7 ones.4 + 3 = 7
- Keep the tens the same. Adding ones does not change the tens.2 tens stay the same
- Put the parts together. 20 and 7 make 27.20 + 7 = 27
Check. Take 3 away from 27. You get 24. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 9 + 5 = 14. That is 10 or more ones, so make a new ten.9 + 5 = 14
- Make a new ten. 14 ones is 1 ten and 4 ones.14 = 1 ten and 4 ones
- Add the new ten to the tens. 3 tens and 1 more ten make 4 tens.40
- Put the parts together. 40 and 4 make 44.40 + 4 = 44
Check. Take 5 away from 44. You get 39. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 2 + 8 = 10. That is 10 or more ones, so make a new ten.2 + 8 = 10
- Make a new ten. 10 ones is 1 ten and 0 ones.10 = 1 ten and 0 ones
- Add the new ten to the tens. 6 tens and 1 more ten make 7 tens.70
- Put the parts together. 70 and 0 make 70.70 + 0 = 70
Check. Take 8 away from 70. You get 62. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. Take 4 ones away from 6 ones.6 − 4 = 2
- Keep the tens the same. Taking ones away does not change the tens.4 tens stay the same
- Put the parts together. 40 and 2 make 42.40 + 2 = 42
Check. Add 4 to 42. You get 46. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. You cannot take 8 from 3, so take 1 ten.3 is less than 8
- Exchange 1 ten for 10 ones. 5 tens becomes 4 tens and 13 ones.3 + 10 = 13
- Take the ones away. 13 − 8 = 513 − 8 = 5
- Put the parts together. 40 and 5 make 45.40 + 5 = 45
Check. Add 8 to 45. You get 53. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. You cannot take 6 from 0, so take 1 ten.0 is less than 6
- Exchange 1 ten for 10 ones. 9 tens becomes 8 tens and 10 ones.0 + 10 = 10
- Take the ones away. 10 − 6 = 410 − 6 = 4
- Put the parts together. 80 and 4 make 84.80 + 4 = 84
Check. Add 6 to 84. You get 90. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. 6 + 4 = 10. That is 10 or more ones, so make a new ten.6 + 4 = 10
- Make a new ten. 10 ones is 1 ten and 0 ones.10 = 1 ten and 0 ones
- Add the new ten to the tens. 3 tens and 1 more ten make 4 tens.40
- Put the parts together. 40 and 0 make 40.40 + 0 = 40
Check. Take 4 away from 40. You get 36. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Key words. An exchange swaps 1 ten for 10 ones, or 10 ones for 1 ten.
Method. Work with the ones first. Then keep the tens.
- Look at the ones. You cannot take 7 from 6, so take 1 ten.6 is less than 7
- Exchange 1 ten for 10 ones. 4 tens becomes 3 tens and 16 ones.6 + 10 = 16
- Take the ones away. 16 − 7 = 916 − 7 = 9
- Put the parts together. 30 and 9 make 39.30 + 9 = 39
Check. Add 7 to 39. You get 46. ✓
Watch out. Work with the ones first. If the ones do not fit, take a ten and make ten ones.
Method. Work out the sum or difference, then compare it with what was said.
- Work out 47 + 5. Use a method that you know.47 + 5 = 52
- Compare with the claim. The claim says 52, and that matches.Yes. 47 + 5 = 52
Check. Take 5 away from 52. You get 47. ✓
Watch out. Check the tens first, then the ones. A carry or an exchange is easy to forget.
Method. Work out the sum or difference, then compare it with what was said.
- Work out 25 − 3. Use a method that you know.25 − 3 = 22
- Compare with the claim. The claim says 23, but the answer is 22.No. 25 − 3 = 22
Check. Add 3 to 22. You get 25. ✓
Watch out. Check the tens first, then the ones. A carry or an exchange is easy to forget.