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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 187 · 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. 1.60 − 9 =
  2. 2.329 + 99 =
  3. 3.60 + 9 =
  4. 4.77 − 19 =
  5. 5.612 + 99 =
  6. 6.688 − 99 =
  7. 7.70 + 9 =
  8. 8.34 + 19 =
  9. 9.36 − 9 =
  10. 10.66 + 29 =
  11. 11.79 − 29 =
  12. 12.58 − 29 =
  13. 13.18 − 9 =
  14. 14.343 − 99 =
  15. 15.538 − 99 =
  16. 16.432 + 99 =
  17. 17.627 + 99 =
  18. 18.80 + 9 =
  19. 19.475 − 99 =
  20. 20.78 − 29 =
  21. 21.468 + 99 =
  22. 22.63 − 19 =
  23. 23.58 + 9 =
  24. 24.23 − 9 =
  25. 25.74 + 19 =
  26. 26.21 + 19 =
  27. 27.48 + 9 =
  28. 28.62 + 9 =
  29. 29.41 + 9 =
  30. 30.50 + 9 =
  31. 31.82 − 29 =
  32. 32.62 − 29 =
  33. 33.28 + 19 =
  34. 34.29 − 9 =
  35. 35.734 + 99 =
  36. 36.51 − 29 =
  37. 37.653 − 99 =
  38. 38.108 − 29 =
  39. 39.48 + 19 =
  40. 40.485 + 99 =

Answer key

  1. 51
  2. 428
  3. 69
  4. 58
  5. 711
  6. 589
  7. 79
  8. 53
  9. 27
  10. 95
  11. 50
  12. 29
  13. 9
  14. 244
  15. 439
  16. 531
  17. 726
  18. 89
  19. 376
  20. 49
  21. 567
  22. 44
  23. 67
  24. 14
  25. 93
  26. 40
  27. 57
  28. 71
  29. 50
  30. 59
  31. 53
  32. 33
  33. 47
  34. 20
  35. 833
  36. 22
  37. 554
  38. 79
  39. 67
  40. 584

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