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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 9 · 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. 1.638 + 99 =
  2. 2.381 − 99 =
  3. 3.52 − 29 =
  4. 4.616 + 99 =
  5. 5.73 + 9 =
  6. 6.497 + 99 =
  7. 7.18 + 9 =
  8. 8.71 + 9 =
  9. 9.633 − 99 =
  10. 10.244 + 99 =
  11. 11.54 + 29 =
  12. 12.87 − 19 =
  13. 13.74 + 19 =
  14. 14.545 + 99 =
  15. 15.451 + 99 =
  16. 16.40 − 9 =
  17. 17.791 + 99 =
  18. 18.42 − 19 =
  19. 19.30 + 9 =
  20. 20.74 + 29 =
  21. 21.66 + 29 =
  22. 22.74 − 29 =
  23. 23.42 − 9 =
  24. 24.65 + 29 =
  25. 25.86 − 19 =
  26. 26.39 − 9 =
  27. 27.49 + 29 =
  28. 28.26 + 29 =
  29. 29.49 − 29 =
  30. 30.527 + 99 =
  31. 31.32 − 19 =
  32. 32.60 + 29 =
  33. 33.467 + 99 =
  34. 34.28 + 29 =
  35. 35.59 − 29 =
  36. 36.688 − 99 =
  37. 37.718 − 99 =
  38. 38.82 − 9 =
  39. 39.51 + 19 =
  40. 40.756 − 99 =

Answer key

  1. 737
  2. 282
  3. 23
  4. 715
  5. 82
  6. 596
  7. 27
  8. 80
  9. 534
  10. 343
  11. 83
  12. 68
  13. 93
  14. 644
  15. 550
  16. 31
  17. 890
  18. 23
  19. 39
  20. 103
  21. 95
  22. 45
  23. 33
  24. 94
  25. 67
  26. 30
  27. 78
  28. 55
  29. 20
  30. 626
  31. 13
  32. 89
  33. 566
  34. 57
  35. 30
  36. 589
  37. 619
  38. 73
  39. 70
  40. 657

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