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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 642 · 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. 1.72 + 9 =
  2. 2.509 − 99 =
  3. 3.66 − 9 =
  4. 4.15 − 9 =
  5. 5.89 − 29 =
  6. 6.61 + 19 =
  7. 7.733 − 99 =
  8. 8.42 + 19 =
  9. 9.321 + 99 =
  10. 10.70 + 19 =
  11. 11.41 + 9 =
  12. 12.19 + 29 =
  13. 13.73 − 19 =
  14. 14.47 − 9 =
  15. 15.66 + 29 =
  16. 16.35 + 19 =
  17. 17.77 + 29 =
  18. 18.298 + 99 =
  19. 19.682 + 99 =
  20. 20.34 − 9 =
  21. 21.32 + 29 =
  22. 22.711 − 99 =
  23. 23.45 − 9 =
  24. 24.717 + 99 =
  25. 25.44 − 9 =
  26. 26.52 + 29 =
  27. 27.46 − 9 =
  28. 28.36 − 19 =
  29. 29.42 + 9 =
  30. 30.72 − 9 =
  31. 31.94 − 29 =
  32. 32.30 − 9 =
  33. 33.25 − 19 =
  34. 34.61 − 19 =
  35. 35.16 + 19 =
  36. 36.75 + 29 =
  37. 37.321 − 99 =
  38. 38.31 − 19 =
  39. 39.30 + 19 =
  40. 40.660 − 99 =

Answer key

  1. 81
  2. 410
  3. 57
  4. 6
  5. 60
  6. 80
  7. 634
  8. 61
  9. 420
  10. 89
  11. 50
  12. 48
  13. 54
  14. 38
  15. 95
  16. 54
  17. 106
  18. 397
  19. 781
  20. 25
  21. 61
  22. 612
  23. 36
  24. 816
  25. 35
  26. 81
  27. 37
  28. 17
  29. 51
  30. 63
  31. 65
  32. 21
  33. 6
  34. 42
  35. 35
  36. 104
  37. 222
  38. 12
  39. 49
  40. 561

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