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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 345 · 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. 1.41 − 9 =
  2. 2.65 − 9 =
  3. 3.13 + 29 =
  4. 4.17 + 19 =
  5. 5.879 − 99 =
  6. 6.23 + 9 =
  7. 7.72 + 9 =
  8. 8.101 − 29 =
  9. 9.86 − 19 =
  10. 10.647 − 99 =
  11. 11.98 − 29 =
  12. 12.54 − 9 =
  13. 13.46 + 19 =
  14. 14.36 − 9 =
  15. 15.49 − 9 =
  16. 16.893 − 99 =
  17. 17.696 + 99 =
  18. 18.785 − 99 =
  19. 19.29 − 19 =
  20. 20.25 + 29 =
  21. 21.65 + 29 =
  22. 22.32 + 9 =
  23. 23.42 − 9 =
  24. 24.409 + 99 =
  25. 25.57 − 19 =
  26. 26.36 − 29 =
  27. 27.38 − 19 =
  28. 28.14 + 29 =
  29. 29.790 − 99 =
  30. 30.21 + 9 =
  31. 31.49 − 29 =
  32. 32.611 + 99 =
  33. 33.30 + 19 =
  34. 34.50 + 29 =
  35. 35.702 − 99 =
  36. 36.96 − 29 =
  37. 37.77 − 19 =
  38. 38.26 − 19 =
  39. 39.43 + 19 =
  40. 40.17 − 9 =

Answer key

  1. 32
  2. 56
  3. 42
  4. 36
  5. 780
  6. 32
  7. 81
  8. 72
  9. 67
  10. 548
  11. 69
  12. 45
  13. 65
  14. 27
  15. 40
  16. 794
  17. 795
  18. 686
  19. 10
  20. 54
  21. 94
  22. 41
  23. 33
  24. 508
  25. 38
  26. 7
  27. 19
  28. 43
  29. 691
  30. 30
  31. 20
  32. 710
  33. 49
  34. 79
  35. 603
  36. 67
  37. 58
  38. 7
  39. 62
  40. 8

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