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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 510 · 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. 1.566 + 99 =
  2. 2.63 + 9 =
  3. 3.42 − 9 =
  4. 4.770 + 99 =
  5. 5.54 − 29 =
  6. 6.16 + 19 =
  7. 7.81 − 9 =
  8. 8.64 + 9 =
  9. 9.31 + 29 =
  10. 10.812 − 99 =
  11. 11.40 + 29 =
  12. 12.19 + 29 =
  13. 13.62 + 9 =
  14. 14.51 − 19 =
  15. 15.47 − 19 =
  16. 16.43 + 19 =
  17. 17.511 − 99 =
  18. 18.105 − 29 =
  19. 19.67 − 19 =
  20. 20.889 − 99 =
  21. 21.716 − 99 =
  22. 22.30 − 19 =
  23. 23.540 − 99 =
  24. 24.698 + 99 =
  25. 25.76 − 19 =
  26. 26.20 + 29 =
  27. 27.37 + 29 =
  28. 28.130 + 99 =
  29. 29.34 + 19 =
  30. 30.52 − 19 =
  31. 31.78 − 9 =
  32. 32.772 − 99 =
  33. 33.99 − 19 =
  34. 34.49 − 9 =
  35. 35.76 − 29 =
  36. 36.73 + 29 =
  37. 37.25 − 9 =
  38. 38.37 + 9 =
  39. 39.66 + 9 =
  40. 40.283 + 99 =

Answer key

  1. 665
  2. 72
  3. 33
  4. 869
  5. 25
  6. 35
  7. 72
  8. 73
  9. 60
  10. 713
  11. 69
  12. 48
  13. 71
  14. 32
  15. 28
  16. 62
  17. 412
  18. 76
  19. 48
  20. 790
  21. 617
  22. 11
  23. 441
  24. 797
  25. 57
  26. 49
  27. 66
  28. 229
  29. 53
  30. 33
  31. 69
  32. 673
  33. 80
  34. 40
  35. 47
  36. 102
  37. 16
  38. 46
  39. 75
  40. 382

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