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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 17 · 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. 1.645 + 99 =
  2. 2.55 − 19 =
  3. 3.43 + 19 =
  4. 4.31 + 19 =
  5. 5.109 − 29 =
  6. 6.15 + 19 =
  7. 7.50 − 9 =
  8. 8.75 + 19 =
  9. 9.125 + 99 =
  10. 10.16 + 29 =
  11. 11.12 − 9 =
  12. 12.77 − 9 =
  13. 13.73 + 19 =
  14. 14.78 − 19 =
  15. 15.33 + 29 =
  16. 16.572 + 99 =
  17. 17.64 + 9 =
  18. 18.47 + 19 =
  19. 19.319 + 99 =
  20. 20.81 − 19 =
  21. 21.35 − 9 =
  22. 22.654 + 99 =
  23. 23.776 − 99 =
  24. 24.57 + 9 =
  25. 25.17 + 29 =
  26. 26.663 − 99 =
  27. 27.83 − 9 =
  28. 28.33 − 19 =
  29. 29.46 + 19 =
  30. 30.58 + 9 =
  31. 31.57 + 19 =
  32. 32.26 + 29 =
  33. 33.56 − 29 =
  34. 34.802 − 99 =
  35. 35.76 + 19 =
  36. 36.78 + 29 =
  37. 37.296 + 99 =
  38. 38.32 + 29 =
  39. 39.551 − 99 =
  40. 40.68 + 9 =

Answer key

  1. 744
  2. 36
  3. 62
  4. 50
  5. 80
  6. 34
  7. 41
  8. 94
  9. 224
  10. 45
  11. 3
  12. 68
  13. 92
  14. 59
  15. 62
  16. 671
  17. 73
  18. 66
  19. 418
  20. 62
  21. 26
  22. 753
  23. 677
  24. 66
  25. 46
  26. 564
  27. 74
  28. 14
  29. 65
  30. 67
  31. 76
  32. 55
  33. 27
  34. 703
  35. 95
  36. 107
  37. 395
  38. 61
  39. 452
  40. 77

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