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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 139 · 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. 1.77 − 19 =
  2. 2.671 + 99 =
  3. 3.617 − 99 =
  4. 4.34 + 9 =
  5. 5.54 + 19 =
  6. 6.29 + 19 =
  7. 7.32 + 19 =
  8. 8.25 + 29 =
  9. 9.504 + 99 =
  10. 10.45 + 19 =
  11. 11.20 + 19 =
  12. 12.31 + 29 =
  13. 13.41 − 9 =
  14. 14.476 + 99 =
  15. 15.15 + 9 =
  16. 16.25 + 9 =
  17. 17.40 + 9 =
  18. 18.53 + 29 =
  19. 19.74 + 9 =
  20. 20.227 + 99 =
  21. 21.50 − 19 =
  22. 22.73 + 19 =
  23. 23.71 + 9 =
  24. 24.22 − 19 =
  25. 25.39 + 19 =
  26. 26.61 + 19 =
  27. 27.73 + 9 =
  28. 28.238 − 99 =
  29. 29.69 − 19 =
  30. 30.49 + 29 =
  31. 31.161 + 99 =
  32. 32.74 − 9 =
  33. 33.623 + 99 =
  34. 34.39 − 9 =
  35. 35.33 + 9 =
  36. 36.668 + 99 =
  37. 37.33 + 19 =
  38. 38.82 − 9 =
  39. 39.59 − 9 =
  40. 40.31 − 9 =

Answer key

  1. 58
  2. 770
  3. 518
  4. 43
  5. 73
  6. 48
  7. 51
  8. 54
  9. 603
  10. 64
  11. 39
  12. 60
  13. 32
  14. 575
  15. 24
  16. 34
  17. 49
  18. 82
  19. 83
  20. 326
  21. 31
  22. 92
  23. 80
  24. 3
  25. 58
  26. 80
  27. 82
  28. 139
  29. 50
  30. 78
  31. 260
  32. 65
  33. 722
  34. 30
  35. 42
  36. 767
  37. 52
  38. 73
  39. 50
  40. 22

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