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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 725 · 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. 1.66 + 29 =
  2. 2.12 + 9 =
  3. 3.354 − 99 =
  4. 4.471 + 99 =
  5. 5.212 + 99 =
  6. 6.239 + 99 =
  7. 7.67 + 19 =
  8. 8.52 + 9 =
  9. 9.30 + 9 =
  10. 10.732 + 99 =
  11. 11.37 − 19 =
  12. 12.22 − 9 =
  13. 13.417 − 99 =
  14. 14.421 − 99 =
  15. 15.41 + 29 =
  16. 16.59 − 9 =
  17. 17.35 − 19 =
  18. 18.73 − 9 =
  19. 19.16 + 9 =
  20. 20.289 − 99 =
  21. 21.186 − 99 =
  22. 22.39 + 19 =
  23. 23.61 + 29 =
  24. 24.627 − 99 =
  25. 25.73 + 9 =
  26. 26.26 + 19 =
  27. 27.781 − 99 =
  28. 28.64 − 19 =
  29. 29.36 + 9 =
  30. 30.346 − 99 =
  31. 31.52 − 29 =
  32. 32.213 − 99 =
  33. 33.298 − 99 =
  34. 34.37 + 9 =
  35. 35.89 − 9 =
  36. 36.24 + 19 =
  37. 37.68 − 29 =
  38. 38.63 + 9 =
  39. 39.18 + 9 =
  40. 40.71 − 29 =

Answer key

  1. 95
  2. 21
  3. 255
  4. 570
  5. 311
  6. 338
  7. 86
  8. 61
  9. 39
  10. 831
  11. 18
  12. 13
  13. 318
  14. 322
  15. 70
  16. 50
  17. 16
  18. 64
  19. 25
  20. 190
  21. 87
  22. 58
  23. 90
  24. 528
  25. 82
  26. 45
  27. 682
  28. 45
  29. 45
  30. 247
  31. 23
  32. 114
  33. 199
  34. 46
  35. 80
  36. 43
  37. 39
  38. 72
  39. 27
  40. 42

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