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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 287 · 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. 1.511 + 99 =
  2. 2.106 − 29 =
  3. 3.53 + 9 =
  4. 4.69 − 29 =
  5. 5.38 + 19 =
  6. 6.198 − 99 =
  7. 7.16 + 19 =
  8. 8.91 − 29 =
  9. 9.19 + 29 =
  10. 10.19 − 9 =
  11. 11.39 + 29 =
  12. 12.38 + 29 =
  13. 13.70 + 19 =
  14. 14.389 + 99 =
  15. 15.218 − 99 =
  16. 16.44 − 29 =
  17. 17.618 + 99 =
  18. 18.54 − 9 =
  19. 19.604 − 99 =
  20. 20.64 − 9 =
  21. 21.78 − 19 =
  22. 22.29 + 29 =
  23. 23.30 + 19 =
  24. 24.295 − 99 =
  25. 25.34 + 29 =
  26. 26.56 + 29 =
  27. 27.66 − 9 =
  28. 28.74 + 9 =
  29. 29.489 − 99 =
  30. 30.36 − 9 =
  31. 31.31 + 29 =
  32. 32.25 + 9 =
  33. 33.61 + 29 =
  34. 34.182 + 99 =
  35. 35.49 + 19 =
  36. 36.55 + 9 =
  37. 37.48 + 29 =
  38. 38.47 + 19 =
  39. 39.12 + 19 =
  40. 40.227 − 99 =

Answer key

  1. 610
  2. 77
  3. 62
  4. 40
  5. 57
  6. 99
  7. 35
  8. 62
  9. 48
  10. 10
  11. 68
  12. 67
  13. 89
  14. 488
  15. 119
  16. 15
  17. 717
  18. 45
  19. 505
  20. 55
  21. 59
  22. 58
  23. 49
  24. 196
  25. 63
  26. 85
  27. 57
  28. 83
  29. 390
  30. 27
  31. 60
  32. 34
  33. 90
  34. 281
  35. 68
  36. 64
  37. 77
  38. 66
  39. 31
  40. 128

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