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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 278 · 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. 1.40 − 29 =
  2. 2.29 − 9 =
  3. 3.21 + 29 =
  4. 4.30 + 29 =
  5. 5.19 − 9 =
  6. 6.81 − 19 =
  7. 7.819 − 99 =
  8. 8.107 − 29 =
  9. 9.72 − 9 =
  10. 10.47 − 29 =
  11. 11.204 + 99 =
  12. 12.62 + 19 =
  13. 13.370 + 99 =
  14. 14.39 − 19 =
  15. 15.35 + 19 =
  16. 16.24 + 19 =
  17. 17.34 + 9 =
  18. 18.45 + 9 =
  19. 19.78 − 9 =
  20. 20.76 − 19 =
  21. 21.68 − 9 =
  22. 22.89 − 19 =
  23. 23.404 + 99 =
  24. 24.35 + 9 =
  25. 25.40 + 9 =
  26. 26.16 + 9 =
  27. 27.403 − 99 =
  28. 28.18 + 29 =
  29. 29.794 − 99 =
  30. 30.61 − 19 =
  31. 31.77 − 19 =
  32. 32.82 − 29 =
  33. 33.55 − 19 =
  34. 34.32 + 29 =
  35. 35.21 + 9 =
  36. 36.413 + 99 =
  37. 37.43 − 19 =
  38. 38.50 + 29 =
  39. 39.704 + 99 =
  40. 40.789 − 99 =

Answer key

  1. 11
  2. 20
  3. 50
  4. 59
  5. 10
  6. 62
  7. 720
  8. 78
  9. 63
  10. 18
  11. 303
  12. 81
  13. 469
  14. 20
  15. 54
  16. 43
  17. 43
  18. 54
  19. 69
  20. 57
  21. 59
  22. 70
  23. 503
  24. 44
  25. 49
  26. 25
  27. 304
  28. 47
  29. 695
  30. 42
  31. 58
  32. 53
  33. 36
  34. 61
  35. 30
  36. 512
  37. 24
  38. 79
  39. 803
  40. 690

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