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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 521 · 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. 1.304 + 99 =
  2. 2.75 − 19 =
  3. 3.59 + 29 =
  4. 4.352 + 99 =
  5. 5.42 + 29 =
  6. 6.200 − 99 =
  7. 7.45 − 9 =
  8. 8.82 − 29 =
  9. 9.28 + 9 =
  10. 10.79 − 29 =
  11. 11.31 + 19 =
  12. 12.70 + 9 =
  13. 13.27 + 9 =
  14. 14.56 + 19 =
  15. 15.98 − 29 =
  16. 16.25 − 9 =
  17. 17.79 + 9 =
  18. 18.72 + 29 =
  19. 19.572 − 99 =
  20. 20.708 − 99 =
  21. 21.413 − 99 =
  22. 22.34 − 9 =
  23. 23.61 − 9 =
  24. 24.38 − 29 =
  25. 25.677 − 99 =
  26. 26.657 + 99 =
  27. 27.59 − 9 =
  28. 28.16 + 29 =
  29. 29.62 − 19 =
  30. 30.26 − 9 =
  31. 31.48 − 9 =
  32. 32.33 + 19 =
  33. 33.630 + 99 =
  34. 34.81 − 29 =
  35. 35.15 + 19 =
  36. 36.80 + 9 =
  37. 37.29 + 9 =
  38. 38.71 − 29 =
  39. 39.70 − 19 =
  40. 40.56 − 19 =

Answer key

  1. 403
  2. 56
  3. 88
  4. 451
  5. 71
  6. 101
  7. 36
  8. 53
  9. 37
  10. 50
  11. 50
  12. 79
  13. 36
  14. 75
  15. 69
  16. 16
  17. 88
  18. 101
  19. 473
  20. 609
  21. 314
  22. 25
  23. 52
  24. 9
  25. 578
  26. 756
  27. 50
  28. 45
  29. 43
  30. 17
  31. 39
  32. 52
  33. 729
  34. 52
  35. 34
  36. 89
  37. 38
  38. 42
  39. 51
  40. 37

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