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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 825 · 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. 1.443 − 99 =
  2. 2.70 + 9 =
  3. 3.95 − 19 =
  4. 4.37 − 19 =
  5. 5.56 − 9 =
  6. 6.641 + 99 =
  7. 7.37 + 29 =
  8. 8.20 + 19 =
  9. 9.26 + 29 =
  10. 10.23 + 19 =
  11. 11.79 + 29 =
  12. 12.35 − 9 =
  13. 13.58 − 19 =
  14. 14.585 − 99 =
  15. 15.58 + 9 =
  16. 16.61 + 29 =
  17. 17.21 + 29 =
  18. 18.89 − 9 =
  19. 19.72 + 9 =
  20. 20.20 + 9 =
  21. 21.38 + 9 =
  22. 22.109 + 99 =
  23. 23.59 + 9 =
  24. 24.868 − 99 =
  25. 25.44 + 9 =
  26. 26.139 + 99 =
  27. 27.395 + 99 =
  28. 28.47 + 19 =
  29. 29.75 + 29 =
  30. 30.202 − 99 =
  31. 31.373 − 99 =
  32. 32.56 + 29 =
  33. 33.64 + 29 =
  34. 34.64 + 19 =
  35. 35.687 − 99 =
  36. 36.37 − 9 =
  37. 37.581 + 99 =
  38. 38.71 + 19 =
  39. 39.43 − 9 =
  40. 40.27 − 9 =

Answer key

  1. 344
  2. 79
  3. 76
  4. 18
  5. 47
  6. 740
  7. 66
  8. 39
  9. 55
  10. 42
  11. 108
  12. 26
  13. 39
  14. 486
  15. 67
  16. 90
  17. 50
  18. 80
  19. 81
  20. 29
  21. 47
  22. 208
  23. 68
  24. 769
  25. 53
  26. 238
  27. 494
  28. 66
  29. 104
  30. 103
  31. 274
  32. 85
  33. 93
  34. 83
  35. 588
  36. 28
  37. 680
  38. 90
  39. 34
  40. 18

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