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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 412 · 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. 1.31 + 29 =
  2. 2.162 − 99 =
  3. 3.645 + 99 =
  4. 4.474 + 99 =
  5. 5.74 − 9 =
  6. 6.29 − 9 =
  7. 7.66 + 29 =
  8. 8.72 + 9 =
  9. 9.20 + 9 =
  10. 10.657 − 99 =
  11. 11.62 + 19 =
  12. 12.61 + 29 =
  13. 13.608 − 99 =
  14. 14.24 + 29 =
  15. 15.31 + 9 =
  16. 16.241 + 99 =
  17. 17.76 + 19 =
  18. 18.150 + 99 =
  19. 19.16 − 9 =
  20. 20.32 + 29 =
  21. 21.402 + 99 =
  22. 22.865 − 99 =
  23. 23.74 + 19 =
  24. 24.524 − 99 =
  25. 25.26 + 29 =
  26. 26.76 − 9 =
  27. 27.63 − 29 =
  28. 28.275 + 99 =
  29. 29.453 − 99 =
  30. 30.200 + 99 =
  31. 31.547 − 99 =
  32. 32.67 + 29 =
  33. 33.41 − 29 =
  34. 34.98 − 19 =
  35. 35.62 + 9 =
  36. 36.37 − 29 =
  37. 37.12 + 9 =
  38. 38.48 + 9 =
  39. 39.66 − 9 =
  40. 40.34 − 29 =

Answer key

  1. 60
  2. 63
  3. 744
  4. 573
  5. 65
  6. 20
  7. 95
  8. 81
  9. 29
  10. 558
  11. 81
  12. 90
  13. 509
  14. 53
  15. 40
  16. 340
  17. 95
  18. 249
  19. 7
  20. 61
  21. 501
  22. 766
  23. 93
  24. 425
  25. 55
  26. 67
  27. 34
  28. 374
  29. 354
  30. 299
  31. 448
  32. 96
  33. 12
  34. 79
  35. 71
  36. 8
  37. 21
  38. 57
  39. 57
  40. 5

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