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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 172 · 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. 2.47 − 19 =
  3. 3.405 + 99 =
  4. 4.78 + 9 =
  5. 5.285 + 99 =
  6. 6.680 + 99 =
  7. 7.63 + 19 =
  8. 8.30 − 19 =
  9. 9.48 − 29 =
  10. 10.32 + 29 =
  11. 11.77 − 9 =
  12. 12.66 + 9 =
  13. 13.719 − 99 =
  14. 14.524 − 99 =
  15. 15.56 − 19 =
  16. 16.55 − 19 =
  17. 17.84 − 19 =
  18. 18.703 − 99 =
  19. 19.88 − 19 =
  20. 20.644 + 99 =
  21. 21.19 + 9 =
  22. 22.29 − 9 =
  23. 23.17 + 29 =
  24. 24.15 + 19 =
  25. 25.56 + 9 =
  26. 26.352 − 99 =
  27. 27.242 − 99 =
  28. 28.47 − 29 =
  29. 29.107 − 29 =
  30. 30.25 − 9 =
  31. 31.17 + 19 =
  32. 32.43 − 19 =
  33. 33.50 + 29 =
  34. 34.65 − 19 =
  35. 35.505 − 99 =
  36. 36.48 − 9 =
  37. 37.74 − 19 =
  38. 38.34 − 9 =
  39. 39.74 + 9 =
  40. 40.58 − 9 =

Answer key

  1. 3
  2. 28
  3. 504
  4. 87
  5. 384
  6. 779
  7. 82
  8. 11
  9. 19
  10. 61
  11. 68
  12. 75
  13. 620
  14. 425
  15. 37
  16. 36
  17. 65
  18. 604
  19. 69
  20. 743
  21. 28
  22. 20
  23. 46
  24. 34
  25. 65
  26. 253
  27. 143
  28. 18
  29. 78
  30. 16
  31. 36
  32. 24
  33. 79
  34. 46
  35. 406
  36. 39
  37. 55
  38. 25
  39. 83
  40. 49

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