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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 336 · 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. 1.516 + 99 =
  2. 2.17 − 9 =
  3. 3.39 + 9 =
  4. 4.472 − 99 =
  5. 5.21 + 9 =
  6. 6.45 − 9 =
  7. 7.519 + 99 =
  8. 8.50 + 9 =
  9. 9.238 − 99 =
  10. 10.79 − 9 =
  11. 11.639 − 99 =
  12. 12.66 − 19 =
  13. 13.16 + 9 =
  14. 14.22 + 9 =
  15. 15.282 + 99 =
  16. 16.401 + 99 =
  17. 17.64 + 9 =
  18. 18.12 + 29 =
  19. 19.23 + 29 =
  20. 20.69 − 9 =
  21. 21.67 + 29 =
  22. 22.64 + 19 =
  23. 23.551 − 99 =
  24. 24.546 + 99 =
  25. 25.45 + 9 =
  26. 26.79 − 19 =
  27. 27.103 − 29 =
  28. 28.34 − 9 =
  29. 29.67 + 19 =
  30. 30.454 − 99 =
  31. 31.32 + 9 =
  32. 32.17 + 29 =
  33. 33.23 + 19 =
  34. 34.38 + 9 =
  35. 35.16 − 9 =
  36. 36.60 − 19 =
  37. 37.93 − 29 =
  38. 38.50 − 9 =
  39. 39.82 − 29 =
  40. 40.77 − 9 =

Answer key

  1. 615
  2. 8
  3. 48
  4. 373
  5. 30
  6. 36
  7. 618
  8. 59
  9. 139
  10. 70
  11. 540
  12. 47
  13. 25
  14. 31
  15. 381
  16. 500
  17. 73
  18. 41
  19. 52
  20. 60
  21. 96
  22. 83
  23. 452
  24. 645
  25. 54
  26. 60
  27. 74
  28. 25
  29. 86
  30. 355
  31. 41
  32. 46
  33. 42
  34. 47
  35. 7
  36. 41
  37. 64
  38. 41
  39. 53
  40. 68

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