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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 931 · 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. 1.504 + 99 =
  2. 2.34 − 9 =
  3. 3.540 + 99 =
  4. 4.443 + 99 =
  5. 5.94 − 19 =
  6. 6.78 + 29 =
  7. 7.842 − 99 =
  8. 8.30 + 19 =
  9. 9.750 + 99 =
  10. 10.58 + 19 =
  11. 11.71 − 19 =
  12. 12.35 + 9 =
  13. 13.71 + 29 =
  14. 14.51 − 19 =
  15. 15.29 − 9 =
  16. 16.18 + 29 =
  17. 17.16 + 19 =
  18. 18.54 + 19 =
  19. 19.105 − 29 =
  20. 20.39 + 9 =
  21. 21.106 − 29 =
  22. 22.70 + 29 =
  23. 23.792 − 99 =
  24. 24.522 + 99 =
  25. 25.41 − 9 =
  26. 26.19 + 19 =
  27. 27.508 + 99 =
  28. 28.171 − 99 =
  29. 29.589 − 99 =
  30. 30.73 − 9 =
  31. 31.73 + 29 =
  32. 32.12 + 9 =
  33. 33.76 + 29 =
  34. 34.63 + 9 =
  35. 35.72 + 19 =
  36. 36.40 − 9 =
  37. 37.378 − 99 =
  38. 38.33 + 19 =
  39. 39.44 + 29 =
  40. 40.98 − 19 =

Answer key

  1. 603
  2. 25
  3. 639
  4. 542
  5. 75
  6. 107
  7. 743
  8. 49
  9. 849
  10. 77
  11. 52
  12. 44
  13. 100
  14. 32
  15. 20
  16. 47
  17. 35
  18. 73
  19. 76
  20. 48
  21. 77
  22. 99
  23. 693
  24. 621
  25. 32
  26. 38
  27. 607
  28. 72
  29. 490
  30. 64
  31. 102
  32. 21
  33. 105
  34. 72
  35. 91
  36. 31
  37. 279
  38. 52
  39. 73
  40. 79

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