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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 689 · 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. 1.12 + 9 =
  2. 2.71 + 29 =
  3. 3.39 + 19 =
  4. 4.67 + 29 =
  5. 5.78 − 29 =
  6. 6.531 + 99 =
  7. 7.68 + 9 =
  8. 8.244 − 99 =
  9. 9.109 − 29 =
  10. 10.24 + 29 =
  11. 11.67 + 9 =
  12. 12.75 − 9 =
  13. 13.19 + 29 =
  14. 14.691 − 99 =
  15. 15.49 − 9 =
  16. 16.49 − 19 =
  17. 17.79 − 19 =
  18. 18.609 + 99 =
  19. 19.66 − 19 =
  20. 20.515 − 99 =
  21. 21.12 + 19 =
  22. 22.52 − 9 =
  23. 23.62 − 9 =
  24. 24.42 − 29 =
  25. 25.46 + 19 =
  26. 26.16 + 19 =
  27. 27.40 − 9 =
  28. 28.54 − 29 =
  29. 29.77 + 19 =
  30. 30.36 − 19 =
  31. 31.278 + 99 =
  32. 32.73 + 9 =
  33. 33.770 + 99 =
  34. 34.12 + 29 =
  35. 35.65 − 19 =
  36. 36.76 + 19 =
  37. 37.17 + 9 =
  38. 38.221 − 99 =
  39. 39.27 + 19 =
  40. 40.28 + 9 =

Answer key

  1. 21
  2. 100
  3. 58
  4. 96
  5. 49
  6. 630
  7. 77
  8. 145
  9. 80
  10. 53
  11. 76
  12. 66
  13. 48
  14. 592
  15. 40
  16. 30
  17. 60
  18. 708
  19. 47
  20. 416
  21. 31
  22. 43
  23. 53
  24. 13
  25. 65
  26. 35
  27. 31
  28. 25
  29. 96
  30. 17
  31. 377
  32. 82
  33. 869
  34. 41
  35. 46
  36. 95
  37. 26
  38. 122
  39. 46
  40. 37

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