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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 279 · 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. 1.278 − 99 =
  2. 2.598 − 99 =
  3. 3.18 + 29 =
  4. 4.50 + 9 =
  5. 5.73 − 19 =
  6. 6.73 + 9 =
  7. 7.20 − 9 =
  8. 8.41 + 19 =
  9. 9.69 + 29 =
  10. 10.50 + 19 =
  11. 11.12 + 19 =
  12. 12.27 − 9 =
  13. 13.29 − 9 =
  14. 14.83 − 29 =
  15. 15.49 + 9 =
  16. 16.239 − 99 =
  17. 17.33 + 29 =
  18. 18.97 − 19 =
  19. 19.54 − 9 =
  20. 20.68 + 9 =
  21. 21.39 + 9 =
  22. 22.68 − 19 =
  23. 23.41 + 29 =
  24. 24.58 − 19 =
  25. 25.48 − 9 =
  26. 26.26 + 9 =
  27. 27.74 + 29 =
  28. 28.75 − 9 =
  29. 29.52 + 19 =
  30. 30.24 − 9 =
  31. 31.430 − 99 =
  32. 32.57 + 29 =
  33. 33.66 − 29 =
  34. 34.18 + 19 =
  35. 35.28 + 9 =
  36. 36.19 + 9 =
  37. 37.589 + 99 =
  38. 38.30 + 9 =
  39. 39.771 − 99 =
  40. 40.52 + 29 =

Answer key

  1. 179
  2. 499
  3. 47
  4. 59
  5. 54
  6. 82
  7. 11
  8. 60
  9. 98
  10. 69
  11. 31
  12. 18
  13. 20
  14. 54
  15. 58
  16. 140
  17. 62
  18. 78
  19. 45
  20. 77
  21. 48
  22. 49
  23. 70
  24. 39
  25. 39
  26. 35
  27. 103
  28. 66
  29. 71
  30. 15
  31. 331
  32. 86
  33. 37
  34. 37
  35. 37
  36. 28
  37. 688
  38. 39
  39. 672
  40. 81

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