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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 366 · 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. 1.42 + 29 =
  2. 2.83 − 29 =
  3. 3.314 − 99 =
  4. 4.592 + 99 =
  5. 5.37 − 29 =
  6. 6.273 + 99 =
  7. 7.76 − 29 =
  8. 8.25 + 19 =
  9. 9.91 − 29 =
  10. 10.63 − 9 =
  11. 11.78 + 9 =
  12. 12.54 − 19 =
  13. 13.20 − 9 =
  14. 14.57 + 9 =
  15. 15.72 − 19 =
  16. 16.61 − 19 =
  17. 17.84 − 9 =
  18. 18.365 − 99 =
  19. 19.223 − 99 =
  20. 20.225 + 99 =
  21. 21.56 − 29 =
  22. 22.53 + 19 =
  23. 23.38 + 9 =
  24. 24.44 + 9 =
  25. 25.67 − 19 =
  26. 26.67 − 29 =
  27. 27.26 + 19 =
  28. 28.150 + 99 =
  29. 29.47 + 19 =
  30. 30.33 − 9 =
  31. 31.233 + 99 =
  32. 32.89 − 9 =
  33. 33.62 + 19 =
  34. 34.33 + 29 =
  35. 35.324 − 99 =
  36. 36.602 + 99 =
  37. 37.23 − 19 =
  38. 38.17 + 19 =
  39. 39.36 − 29 =
  40. 40.869 − 99 =

Answer key

  1. 71
  2. 54
  3. 215
  4. 691
  5. 8
  6. 372
  7. 47
  8. 44
  9. 62
  10. 54
  11. 87
  12. 35
  13. 11
  14. 66
  15. 53
  16. 42
  17. 75
  18. 266
  19. 124
  20. 324
  21. 27
  22. 72
  23. 47
  24. 53
  25. 48
  26. 38
  27. 45
  28. 249
  29. 66
  30. 24
  31. 332
  32. 80
  33. 81
  34. 62
  35. 225
  36. 701
  37. 4
  38. 36
  39. 7
  40. 770

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