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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 624 · 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. 1.407 − 99 =
  2. 2.39 + 29 =
  3. 3.26 + 9 =
  4. 4.682 + 99 =
  5. 5.45 + 19 =
  6. 6.25 + 19 =
  7. 7.33 + 29 =
  8. 8.54 + 9 =
  9. 9.23 + 9 =
  10. 10.32 + 29 =
  11. 11.77 + 9 =
  12. 12.585 − 99 =
  13. 13.426 + 99 =
  14. 14.58 + 29 =
  15. 15.425 − 99 =
  16. 16.75 + 29 =
  17. 17.444 − 99 =
  18. 18.65 + 19 =
  19. 19.63 + 29 =
  20. 20.21 + 9 =
  21. 21.28 + 9 =
  22. 22.126 + 99 =
  23. 23.40 − 19 =
  24. 24.28 + 29 =
  25. 25.52 + 29 =
  26. 26.643 − 99 =
  27. 27.57 + 19 =
  28. 28.22 + 9 =
  29. 29.63 + 9 =
  30. 30.607 − 99 =
  31. 31.44 + 19 =
  32. 32.28 + 19 =
  33. 33.44 − 29 =
  34. 34.37 + 19 =
  35. 35.732 − 99 =
  36. 36.218 + 99 =
  37. 37.314 − 99 =
  38. 38.74 − 9 =
  39. 39.896 − 99 =
  40. 40.182 + 99 =

Answer key

  1. 308
  2. 68
  3. 35
  4. 781
  5. 64
  6. 44
  7. 62
  8. 63
  9. 32
  10. 61
  11. 86
  12. 486
  13. 525
  14. 87
  15. 326
  16. 104
  17. 345
  18. 84
  19. 92
  20. 30
  21. 37
  22. 225
  23. 21
  24. 57
  25. 81
  26. 544
  27. 76
  28. 31
  29. 72
  30. 508
  31. 63
  32. 47
  33. 15
  34. 56
  35. 633
  36. 317
  37. 215
  38. 65
  39. 797
  40. 281

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