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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 330 · 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. 1.61 − 9 =
  2. 2.648 + 99 =
  3. 3.481 + 99 =
  4. 4.170 + 99 =
  5. 5.454 − 99 =
  6. 6.22 + 19 =
  7. 7.87 − 9 =
  8. 8.19 + 29 =
  9. 9.78 + 29 =
  10. 10.84 − 29 =
  11. 11.65 − 19 =
  12. 12.121 + 99 =
  13. 13.82 − 9 =
  14. 14.525 + 99 =
  15. 15.16 − 9 =
  16. 16.72 − 29 =
  17. 17.887 − 99 =
  18. 18.292 + 99 =
  19. 19.17 + 29 =
  20. 20.71 + 29 =
  21. 21.617 + 99 =
  22. 22.719 + 99 =
  23. 23.33 + 9 =
  24. 24.497 + 99 =
  25. 25.18 + 19 =
  26. 26.48 + 9 =
  27. 27.31 + 19 =
  28. 28.26 + 9 =
  29. 29.41 + 9 =
  30. 30.65 + 9 =
  31. 31.494 − 99 =
  32. 32.436 − 99 =
  33. 33.51 + 9 =
  34. 34.48 + 19 =
  35. 35.75 + 29 =
  36. 36.37 − 9 =
  37. 37.28 − 9 =
  38. 38.864 − 99 =
  39. 39.32 + 29 =
  40. 40.18 + 29 =

Answer key

  1. 52
  2. 747
  3. 580
  4. 269
  5. 355
  6. 41
  7. 78
  8. 48
  9. 107
  10. 55
  11. 46
  12. 220
  13. 73
  14. 624
  15. 7
  16. 43
  17. 788
  18. 391
  19. 46
  20. 100
  21. 716
  22. 818
  23. 42
  24. 596
  25. 37
  26. 57
  27. 50
  28. 35
  29. 50
  30. 74
  31. 395
  32. 337
  33. 60
  34. 67
  35. 104
  36. 28
  37. 19
  38. 765
  39. 61
  40. 47

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