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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 264 · 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. 1.81 − 29 =
  2. 2.180 + 99 =
  3. 3.24 + 9 =
  4. 4.420 − 99 =
  5. 5.78 − 29 =
  6. 6.328 − 99 =
  7. 7.20 − 9 =
  8. 8.470 + 99 =
  9. 9.52 + 29 =
  10. 10.23 + 9 =
  11. 11.16 + 9 =
  12. 12.33 + 19 =
  13. 13.505 − 99 =
  14. 14.385 + 99 =
  15. 15.189 − 99 =
  16. 16.39 + 9 =
  17. 17.38 + 19 =
  18. 18.79 − 19 =
  19. 19.34 − 19 =
  20. 20.38 − 19 =
  21. 21.56 − 29 =
  22. 22.51 + 19 =
  23. 23.25 + 29 =
  24. 24.869 − 99 =
  25. 25.290 + 99 =
  26. 26.12 + 9 =
  27. 27.255 − 99 =
  28. 28.22 − 9 =
  29. 29.94 − 29 =
  30. 30.476 + 99 =
  31. 31.748 + 99 =
  32. 32.51 + 9 =
  33. 33.58 + 19 =
  34. 34.64 + 29 =
  35. 35.18 + 19 =
  36. 36.49 + 9 =
  37. 37.152 + 99 =
  38. 38.30 + 29 =
  39. 39.775 + 99 =
  40. 40.235 − 99 =

Answer key

  1. 52
  2. 279
  3. 33
  4. 321
  5. 49
  6. 229
  7. 11
  8. 569
  9. 81
  10. 32
  11. 25
  12. 52
  13. 406
  14. 484
  15. 90
  16. 48
  17. 57
  18. 60
  19. 15
  20. 19
  21. 27
  22. 70
  23. 54
  24. 770
  25. 389
  26. 21
  27. 156
  28. 13
  29. 65
  30. 575
  31. 847
  32. 60
  33. 77
  34. 93
  35. 37
  36. 58
  37. 251
  38. 59
  39. 874
  40. 136

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