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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 517 · 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. 1.259 − 99 =
  2. 2.13 − 9 =
  3. 3.507 + 99 =
  4. 4.403 + 99 =
  5. 5.421 − 99 =
  6. 6.65 + 29 =
  7. 7.96 − 19 =
  8. 8.41 + 29 =
  9. 9.384 + 99 =
  10. 10.28 − 9 =
  11. 11.62 + 29 =
  12. 12.171 + 99 =
  13. 13.471 + 99 =
  14. 14.488 + 99 =
  15. 15.497 − 99 =
  16. 16.34 − 29 =
  17. 17.70 − 19 =
  18. 18.287 + 99 =
  19. 19.59 − 19 =
  20. 20.74 + 29 =
  21. 21.673 + 99 =
  22. 22.80 + 9 =
  23. 23.81 − 29 =
  24. 24.22 + 19 =
  25. 25.165 + 99 =
  26. 26.29 − 9 =
  27. 27.173 − 99 =
  28. 28.42 − 19 =
  29. 29.68 + 29 =
  30. 30.76 + 29 =
  31. 31.44 − 19 =
  32. 32.25 + 29 =
  33. 33.79 − 9 =
  34. 34.66 − 19 =
  35. 35.68 + 19 =
  36. 36.94 − 19 =
  37. 37.60 + 29 =
  38. 38.797 + 99 =
  39. 39.576 + 99 =
  40. 40.85 − 9 =

Answer key

  1. 160
  2. 4
  3. 606
  4. 502
  5. 322
  6. 94
  7. 77
  8. 70
  9. 483
  10. 19
  11. 91
  12. 270
  13. 570
  14. 587
  15. 398
  16. 5
  17. 51
  18. 386
  19. 40
  20. 103
  21. 772
  22. 89
  23. 52
  24. 41
  25. 264
  26. 20
  27. 74
  28. 23
  29. 97
  30. 105
  31. 25
  32. 54
  33. 70
  34. 47
  35. 87
  36. 75
  37. 89
  38. 896
  39. 675
  40. 76

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