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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 175 · 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. 1.180 + 99 =
  2. 2.23 − 9 =
  3. 3.185 + 99 =
  4. 4.70 + 19 =
  5. 5.78 + 29 =
  6. 6.37 − 9 =
  7. 7.50 − 29 =
  8. 8.77 + 29 =
  9. 9.71 − 19 =
  10. 10.67 − 9 =
  11. 11.61 − 9 =
  12. 12.98 − 19 =
  13. 13.273 + 99 =
  14. 14.64 + 9 =
  15. 15.74 + 19 =
  16. 16.72 + 19 =
  17. 17.57 + 19 =
  18. 18.78 + 9 =
  19. 19.50 − 19 =
  20. 20.434 − 99 =
  21. 21.249 − 99 =
  22. 22.763 − 99 =
  23. 23.28 − 19 =
  24. 24.12 + 9 =
  25. 25.49 + 19 =
  26. 26.38 − 19 =
  27. 27.29 + 19 =
  28. 28.59 + 9 =
  29. 29.42 + 29 =
  30. 30.30 + 9 =
  31. 31.21 + 9 =
  32. 32.82 − 19 =
  33. 33.56 + 29 =
  34. 34.224 + 99 =
  35. 35.33 + 9 =
  36. 36.93 − 29 =
  37. 37.36 + 29 =
  38. 38.58 − 9 =
  39. 39.74 − 9 =
  40. 40.91 − 29 =

Answer key

  1. 279
  2. 14
  3. 284
  4. 89
  5. 107
  6. 28
  7. 21
  8. 106
  9. 52
  10. 58
  11. 52
  12. 79
  13. 372
  14. 73
  15. 93
  16. 91
  17. 76
  18. 87
  19. 31
  20. 335
  21. 150
  22. 664
  23. 9
  24. 21
  25. 68
  26. 19
  27. 48
  28. 68
  29. 71
  30. 39
  31. 30
  32. 63
  33. 85
  34. 323
  35. 42
  36. 64
  37. 65
  38. 49
  39. 65
  40. 62

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