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Adding 9, 19 and 99 Mental Maths Worksheet

Mental maths lesson 4: Add and take away 9, 19 and 99 · Set 824 · 40 questions
TalentJR

How to do it in your head (Round and adjust): Add 9, 19, 99: add 10, 20, 100, then take 1 away. Take away 9, 19, 99: take away 10, 20, 100, then add 1 back. Ask yourself: did I use too much or too little?

NameDateTime takenScore ___ / 40
  1. 1.390 − 99 =
  2. 2.75 + 9 =
  3. 3.43 − 9 =
  4. 4.636 − 99 =
  5. 5.262 + 99 =
  6. 6.25 − 9 =
  7. 7.64 − 9 =
  8. 8.16 − 9 =
  9. 9.38 + 9 =
  10. 10.53 + 9 =
  11. 11.231 + 99 =
  12. 12.317 + 99 =
  13. 13.69 − 9 =
  14. 14.32 + 19 =
  15. 15.25 + 9 =
  16. 16.38 − 19 =
  17. 17.472 + 99 =
  18. 18.71 + 19 =
  19. 19.22 − 19 =
  20. 20.68 − 19 =
  21. 21.178 + 99 =
  22. 22.581 + 99 =
  23. 23.48 + 29 =
  24. 24.634 − 99 =
  25. 25.203 + 99 =
  26. 26.44 + 9 =
  27. 27.107 − 29 =
  28. 28.26 + 29 =
  29. 29.45 + 29 =
  30. 30.58 − 29 =
  31. 31.41 + 9 =
  32. 32.33 + 29 =
  33. 33.60 + 29 =
  34. 34.735 − 99 =
  35. 35.79 + 9 =
  36. 36.501 − 99 =
  37. 37.39 − 9 =
  38. 38.14 + 19 =
  39. 39.37 − 29 =
  40. 40.78 − 9 =

Answer key

  1. 291
  2. 84
  3. 34
  4. 537
  5. 361
  6. 16
  7. 55
  8. 7
  9. 47
  10. 62
  11. 330
  12. 416
  13. 60
  14. 51
  15. 34
  16. 19
  17. 571
  18. 90
  19. 3
  20. 49
  21. 277
  22. 680
  23. 77
  24. 535
  25. 302
  26. 53
  27. 78
  28. 55
  29. 74
  30. 29
  31. 50
  32. 62
  33. 89
  34. 636
  35. 88
  36. 402
  37. 30
  38. 33
  39. 8
  40. 69

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