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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 42 · 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. 1.750 + 99 =
  2. 2.38 − 9 =
  3. 3.246 − 99 =
  4. 4.27 − 9 =
  5. 5.72 − 29 =
  6. 6.92 − 19 =
  7. 7.60 − 9 =
  8. 8.17 + 9 =
  9. 9.435 − 99 =
  10. 10.784 − 99 =
  11. 11.67 + 9 =
  12. 12.81 − 29 =
  13. 13.41 − 29 =
  14. 14.28 − 19 =
  15. 15.78 − 9 =
  16. 16.94 − 29 =
  17. 17.31 + 9 =
  18. 18.22 + 19 =
  19. 19.67 − 19 =
  20. 20.245 − 99 =
  21. 21.61 + 9 =
  22. 22.26 + 29 =
  23. 23.28 + 9 =
  24. 24.576 + 99 =
  25. 25.51 + 19 =
  26. 26.499 − 99 =
  27. 27.73 + 9 =
  28. 28.171 − 99 =
  29. 29.58 + 9 =
  30. 30.16 − 9 =
  31. 31.409 − 99 =
  32. 32.57 − 29 =
  33. 33.27 + 29 =
  34. 34.12 + 9 =
  35. 35.51 − 9 =
  36. 36.43 − 29 =
  37. 37.52 + 19 =
  38. 38.68 − 29 =
  39. 39.39 + 29 =
  40. 40.57 + 9 =

Answer key

  1. 849
  2. 29
  3. 147
  4. 18
  5. 43
  6. 73
  7. 51
  8. 26
  9. 336
  10. 685
  11. 76
  12. 52
  13. 12
  14. 9
  15. 69
  16. 65
  17. 40
  18. 41
  19. 48
  20. 146
  21. 70
  22. 55
  23. 37
  24. 675
  25. 70
  26. 400
  27. 82
  28. 72
  29. 67
  30. 7
  31. 310
  32. 28
  33. 56
  34. 21
  35. 42
  36. 14
  37. 71
  38. 39
  39. 68
  40. 66

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