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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 108 · 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. 1.47 − 29 =
  2. 2.714 + 99 =
  3. 3.33 + 29 =
  4. 4.31 + 9 =
  5. 5.69 − 19 =
  6. 6.77 + 9 =
  7. 7.441 + 99 =
  8. 8.63 − 19 =
  9. 9.387 + 99 =
  10. 10.785 + 99 =
  11. 11.21 + 29 =
  12. 12.78 − 9 =
  13. 13.94 − 19 =
  14. 14.64 − 19 =
  15. 15.14 + 19 =
  16. 16.35 − 29 =
  17. 17.35 − 19 =
  18. 18.204 − 99 =
  19. 19.61 + 29 =
  20. 20.358 − 99 =
  21. 21.61 + 19 =
  22. 22.89 − 29 =
  23. 23.223 + 99 =
  24. 24.285 + 99 =
  25. 25.62 + 9 =
  26. 26.96 − 19 =
  27. 27.17 − 9 =
  28. 28.472 + 99 =
  29. 29.52 + 9 =
  30. 30.29 + 19 =
  31. 31.43 + 29 =
  32. 32.84 − 29 =
  33. 33.22 + 29 =
  34. 34.425 − 99 =
  35. 35.44 − 19 =
  36. 36.27 + 9 =
  37. 37.84 − 9 =
  38. 38.72 + 9 =
  39. 39.823 − 99 =
  40. 40.13 + 29 =

Answer key

  1. 18
  2. 813
  3. 62
  4. 40
  5. 50
  6. 86
  7. 540
  8. 44
  9. 486
  10. 884
  11. 50
  12. 69
  13. 75
  14. 45
  15. 33
  16. 6
  17. 16
  18. 105
  19. 90
  20. 259
  21. 80
  22. 60
  23. 322
  24. 384
  25. 71
  26. 77
  27. 8
  28. 571
  29. 61
  30. 48
  31. 72
  32. 55
  33. 51
  34. 326
  35. 25
  36. 36
  37. 75
  38. 81
  39. 724
  40. 42

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