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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 36 · 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. 1.59 − 9 =
  2. 2.231 + 99 =
  3. 3.35 + 9 =
  4. 4.63 − 19 =
  5. 5.25 − 9 =
  6. 6.16 + 29 =
  7. 7.67 + 29 =
  8. 8.54 − 9 =
  9. 9.58 + 29 =
  10. 10.66 + 9 =
  11. 11.66 − 9 =
  12. 12.13 + 19 =
  13. 13.57 + 29 =
  14. 14.13 + 29 =
  15. 15.47 − 29 =
  16. 16.71 + 29 =
  17. 17.48 − 29 =
  18. 18.167 − 99 =
  19. 19.210 + 99 =
  20. 20.68 − 9 =
  21. 21.70 − 9 =
  22. 22.40 + 29 =
  23. 23.378 + 99 =
  24. 24.62 − 29 =
  25. 25.315 + 99 =
  26. 26.60 − 9 =
  27. 27.16 + 9 =
  28. 28.474 + 99 =
  29. 29.37 − 19 =
  30. 30.69 − 29 =
  31. 31.792 + 99 =
  32. 32.64 + 19 =
  33. 33.56 + 29 =
  34. 34.90 − 29 =
  35. 35.20 − 9 =
  36. 36.17 − 9 =
  37. 37.388 − 99 =
  38. 38.341 + 99 =
  39. 39.69 + 9 =
  40. 40.516 + 99 =

Answer key

  1. 50
  2. 330
  3. 44
  4. 44
  5. 16
  6. 45
  7. 96
  8. 45
  9. 87
  10. 75
  11. 57
  12. 32
  13. 86
  14. 42
  15. 18
  16. 100
  17. 19
  18. 68
  19. 309
  20. 59
  21. 61
  22. 69
  23. 477
  24. 33
  25. 414
  26. 51
  27. 25
  28. 573
  29. 18
  30. 40
  31. 891
  32. 83
  33. 85
  34. 61
  35. 11
  36. 8
  37. 289
  38. 440
  39. 78
  40. 615

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