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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 199 · 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. 1.729 − 99 =
  2. 2.40 − 29 =
  3. 3.365 + 99 =
  4. 4.412 + 99 =
  5. 5.457 + 99 =
  6. 6.15 + 19 =
  7. 7.49 − 29 =
  8. 8.39 − 9 =
  9. 9.60 + 9 =
  10. 10.92 − 29 =
  11. 11.76 − 19 =
  12. 12.15 + 29 =
  13. 13.77 + 9 =
  14. 14.86 − 9 =
  15. 15.107 − 29 =
  16. 16.593 − 99 =
  17. 17.84 − 19 =
  18. 18.53 + 29 =
  19. 19.710 + 99 =
  20. 20.27 + 9 =
  21. 21.85 − 19 =
  22. 22.35 − 19 =
  23. 23.42 + 9 =
  24. 24.30 − 9 =
  25. 25.31 + 9 =
  26. 26.18 + 29 =
  27. 27.35 + 9 =
  28. 28.29 + 9 =
  29. 29.427 + 99 =
  30. 30.73 + 29 =
  31. 31.35 − 29 =
  32. 32.24 + 29 =
  33. 33.59 + 29 =
  34. 34.14 + 29 =
  35. 35.188 − 99 =
  36. 36.78 + 29 =
  37. 37.203 + 99 =
  38. 38.19 + 29 =
  39. 39.58 + 19 =
  40. 40.37 − 19 =

Answer key

  1. 630
  2. 11
  3. 464
  4. 511
  5. 556
  6. 34
  7. 20
  8. 30
  9. 69
  10. 63
  11. 57
  12. 44
  13. 86
  14. 77
  15. 78
  16. 494
  17. 65
  18. 82
  19. 809
  20. 36
  21. 66
  22. 16
  23. 51
  24. 21
  25. 40
  26. 47
  27. 44
  28. 38
  29. 526
  30. 102
  31. 6
  32. 53
  33. 88
  34. 43
  35. 89
  36. 107
  37. 302
  38. 48
  39. 77
  40. 18

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