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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 103 · 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. 1.55 + 29 =
  2. 2.482 − 99 =
  3. 3.61 − 19 =
  4. 4.588 + 99 =
  5. 5.56 + 9 =
  6. 6.704 + 99 =
  7. 7.18 + 9 =
  8. 8.666 + 99 =
  9. 9.18 − 9 =
  10. 10.24 + 9 =
  11. 11.215 + 99 =
  12. 12.71 − 19 =
  13. 13.50 − 29 =
  14. 14.30 + 9 =
  15. 15.109 − 29 =
  16. 16.16 + 29 =
  17. 17.546 + 99 =
  18. 18.892 − 99 =
  19. 19.533 − 99 =
  20. 20.52 + 19 =
  21. 21.358 − 99 =
  22. 22.58 + 19 =
  23. 23.830 − 99 =
  24. 24.48 + 9 =
  25. 25.471 + 99 =
  26. 26.35 + 9 =
  27. 27.73 − 29 =
  28. 28.71 + 19 =
  29. 29.787 + 99 =
  30. 30.78 + 19 =
  31. 31.280 − 99 =
  32. 32.38 + 9 =
  33. 33.67 + 19 =
  34. 34.64 + 19 =
  35. 35.71 + 29 =
  36. 36.62 + 9 =
  37. 37.213 + 99 =
  38. 38.26 + 9 =
  39. 39.563 − 99 =
  40. 40.77 − 29 =

Answer key

  1. 84
  2. 383
  3. 42
  4. 687
  5. 65
  6. 803
  7. 27
  8. 765
  9. 9
  10. 33
  11. 314
  12. 52
  13. 21
  14. 39
  15. 80
  16. 45
  17. 645
  18. 793
  19. 434
  20. 71
  21. 259
  22. 77
  23. 731
  24. 57
  25. 570
  26. 44
  27. 44
  28. 90
  29. 886
  30. 97
  31. 181
  32. 47
  33. 86
  34. 83
  35. 100
  36. 71
  37. 312
  38. 35
  39. 464
  40. 48

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