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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 317 · 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. 1.820 − 99 =
  2. 2.60 − 9 =
  3. 3.49 − 9 =
  4. 4.42 + 9 =
  5. 5.28 − 9 =
  6. 6.36 + 29 =
  7. 7.265 + 99 =
  8. 8.18 + 19 =
  9. 9.18 + 9 =
  10. 10.521 − 99 =
  11. 11.45 + 9 =
  12. 12.470 + 99 =
  13. 13.72 − 29 =
  14. 14.19 + 9 =
  15. 15.12 + 9 =
  16. 16.84 − 9 =
  17. 17.13 + 29 =
  18. 18.55 + 19 =
  19. 19.42 + 29 =
  20. 20.43 − 9 =
  21. 21.322 − 99 =
  22. 22.17 − 9 =
  23. 23.60 + 9 =
  24. 24.46 + 9 =
  25. 25.43 − 29 =
  26. 26.34 + 9 =
  27. 27.62 + 29 =
  28. 28.203 + 99 =
  29. 29.74 + 29 =
  30. 30.48 + 19 =
  31. 31.68 + 9 =
  32. 32.88 − 19 =
  33. 33.766 + 99 =
  34. 34.751 + 99 =
  35. 35.57 + 19 =
  36. 36.344 − 99 =
  37. 37.47 + 9 =
  38. 38.90 − 29 =
  39. 39.99 − 29 =
  40. 40.77 − 29 =

Answer key

  1. 721
  2. 51
  3. 40
  4. 51
  5. 19
  6. 65
  7. 364
  8. 37
  9. 27
  10. 422
  11. 54
  12. 569
  13. 43
  14. 28
  15. 21
  16. 75
  17. 42
  18. 74
  19. 71
  20. 34
  21. 223
  22. 8
  23. 69
  24. 55
  25. 14
  26. 43
  27. 91
  28. 302
  29. 103
  30. 67
  31. 77
  32. 69
  33. 865
  34. 850
  35. 76
  36. 245
  37. 56
  38. 61
  39. 70
  40. 48

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