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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 789 · 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. 1.456 + 99 =
  2. 2.33 − 29 =
  3. 3.25 + 19 =
  4. 4.54 + 29 =
  5. 5.39 − 29 =
  6. 6.75 − 19 =
  7. 7.65 − 19 =
  8. 8.65 + 9 =
  9. 9.54 − 9 =
  10. 10.96 − 19 =
  11. 11.17 + 9 =
  12. 12.240 + 99 =
  13. 13.18 − 9 =
  14. 14.589 + 99 =
  15. 15.94 − 29 =
  16. 16.43 + 19 =
  17. 17.67 + 19 =
  18. 18.179 + 99 =
  19. 19.83 − 19 =
  20. 20.45 + 19 =
  21. 21.28 + 9 =
  22. 22.83 − 29 =
  23. 23.45 + 29 =
  24. 24.76 + 9 =
  25. 25.670 − 99 =
  26. 26.30 − 9 =
  27. 27.531 − 99 =
  28. 28.828 − 99 =
  29. 29.72 − 19 =
  30. 30.156 + 99 =
  31. 31.37 − 19 =
  32. 32.351 − 99 =
  33. 33.564 + 99 =
  34. 34.24 + 9 =
  35. 35.43 − 29 =
  36. 36.704 + 99 =
  37. 37.77 + 29 =
  38. 38.75 − 29 =
  39. 39.74 + 19 =
  40. 40.62 − 9 =

Answer key

  1. 555
  2. 4
  3. 44
  4. 83
  5. 10
  6. 56
  7. 46
  8. 74
  9. 45
  10. 77
  11. 26
  12. 339
  13. 9
  14. 688
  15. 65
  16. 62
  17. 86
  18. 278
  19. 64
  20. 64
  21. 37
  22. 54
  23. 74
  24. 85
  25. 571
  26. 21
  27. 432
  28. 729
  29. 53
  30. 255
  31. 18
  32. 252
  33. 663
  34. 33
  35. 14
  36. 803
  37. 106
  38. 46
  39. 93
  40. 53

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