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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 138 · 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. 1.363 − 99 =
  2. 2.692 − 99 =
  3. 3.767 − 99 =
  4. 4.31 + 9 =
  5. 5.78 − 29 =
  6. 6.36 + 29 =
  7. 7.77 + 9 =
  8. 8.79 + 19 =
  9. 9.64 − 19 =
  10. 10.724 + 99 =
  11. 11.51 + 9 =
  12. 12.45 − 9 =
  13. 13.86 − 29 =
  14. 14.69 + 29 =
  15. 15.85 − 29 =
  16. 16.23 + 29 =
  17. 17.25 − 9 =
  18. 18.24 − 19 =
  19. 19.14 + 19 =
  20. 20.743 + 99 =
  21. 21.668 − 99 =
  22. 22.48 − 29 =
  23. 23.279 + 99 =
  24. 24.92 − 29 =
  25. 25.68 + 9 =
  26. 26.36 − 19 =
  27. 27.45 − 19 =
  28. 28.699 − 99 =
  29. 29.666 + 99 =
  30. 30.38 + 9 =
  31. 31.53 − 29 =
  32. 32.78 − 19 =
  33. 33.65 + 29 =
  34. 34.494 − 99 =
  35. 35.80 + 29 =
  36. 36.530 − 99 =
  37. 37.81 − 9 =
  38. 38.653 + 99 =
  39. 39.119 + 99 =
  40. 40.70 − 9 =

Answer key

  1. 264
  2. 593
  3. 668
  4. 40
  5. 49
  6. 65
  7. 86
  8. 98
  9. 45
  10. 823
  11. 60
  12. 36
  13. 57
  14. 98
  15. 56
  16. 52
  17. 16
  18. 5
  19. 33
  20. 842
  21. 569
  22. 19
  23. 378
  24. 63
  25. 77
  26. 17
  27. 26
  28. 600
  29. 765
  30. 47
  31. 24
  32. 59
  33. 94
  34. 395
  35. 109
  36. 431
  37. 72
  38. 752
  39. 218
  40. 61

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