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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 225 · 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. 1.375 + 99 =
  2. 2.493 + 99 =
  3. 3.76 − 29 =
  4. 4.76 − 19 =
  5. 5.40 − 29 =
  6. 6.24 + 9 =
  7. 7.51 + 19 =
  8. 8.71 + 9 =
  9. 9.17 − 9 =
  10. 10.516 + 99 =
  11. 11.35 + 9 =
  12. 12.35 − 29 =
  13. 13.31 + 9 =
  14. 14.34 − 9 =
  15. 15.79 + 9 =
  16. 16.82 − 9 =
  17. 17.77 − 9 =
  18. 18.878 − 99 =
  19. 19.69 + 9 =
  20. 20.40 − 19 =
  21. 21.45 − 29 =
  22. 22.66 + 29 =
  23. 23.61 − 19 =
  24. 24.43 + 19 =
  25. 25.348 + 99 =
  26. 26.68 − 9 =
  27. 27.73 + 29 =
  28. 28.155 − 99 =
  29. 29.71 − 29 =
  30. 30.69 + 29 =
  31. 31.15 + 19 =
  32. 32.40 + 29 =
  33. 33.29 + 29 =
  34. 34.38 − 29 =
  35. 35.84 − 29 =
  36. 36.41 + 9 =
  37. 37.109 − 29 =
  38. 38.92 − 19 =
  39. 39.12 + 9 =
  40. 40.30 + 9 =

Answer key

  1. 474
  2. 592
  3. 47
  4. 57
  5. 11
  6. 33
  7. 70
  8. 80
  9. 8
  10. 615
  11. 44
  12. 6
  13. 40
  14. 25
  15. 88
  16. 73
  17. 68
  18. 779
  19. 78
  20. 21
  21. 16
  22. 95
  23. 42
  24. 62
  25. 447
  26. 59
  27. 102
  28. 56
  29. 42
  30. 98
  31. 34
  32. 69
  33. 58
  34. 9
  35. 55
  36. 50
  37. 80
  38. 73
  39. 21
  40. 39

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