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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 844 · 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. 1.793 + 99 =
  2. 2.274 − 99 =
  3. 3.59 + 19 =
  4. 4.90 − 19 =
  5. 5.585 − 99 =
  6. 6.47 + 29 =
  7. 7.106 − 29 =
  8. 8.25 − 9 =
  9. 9.16 + 9 =
  10. 10.68 + 9 =
  11. 11.35 + 9 =
  12. 12.855 − 99 =
  13. 13.43 − 19 =
  14. 14.88 − 29 =
  15. 15.38 − 29 =
  16. 16.53 − 29 =
  17. 17.317 + 99 =
  18. 18.568 + 99 =
  19. 19.29 − 19 =
  20. 20.48 − 9 =
  21. 21.37 + 29 =
  22. 22.35 − 9 =
  23. 23.88 − 9 =
  24. 24.18 + 29 =
  25. 25.63 + 9 =
  26. 26.80 − 9 =
  27. 27.677 − 99 =
  28. 28.66 − 19 =
  29. 29.630 − 99 =
  30. 30.15 + 9 =
  31. 31.529 − 99 =
  32. 32.523 + 99 =
  33. 33.454 + 99 =
  34. 34.17 + 19 =
  35. 35.12 − 9 =
  36. 36.100 − 29 =
  37. 37.44 + 9 =
  38. 38.22 − 9 =
  39. 39.26 − 19 =
  40. 40.36 + 9 =

Answer key

  1. 892
  2. 175
  3. 78
  4. 71
  5. 486
  6. 76
  7. 77
  8. 16
  9. 25
  10. 77
  11. 44
  12. 756
  13. 24
  14. 59
  15. 9
  16. 24
  17. 416
  18. 667
  19. 10
  20. 39
  21. 66
  22. 26
  23. 79
  24. 47
  25. 72
  26. 71
  27. 578
  28. 47
  29. 531
  30. 24
  31. 430
  32. 622
  33. 553
  34. 36
  35. 3
  36. 71
  37. 53
  38. 13
  39. 7
  40. 45

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