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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 457 · 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. 1.38 − 9 =
  2. 2.53 + 19 =
  3. 3.23 − 9 =
  4. 4.245 + 99 =
  5. 5.50 − 29 =
  6. 6.71 + 19 =
  7. 7.27 − 19 =
  8. 8.89 − 9 =
  9. 9.39 − 9 =
  10. 10.82 − 29 =
  11. 11.251 + 99 =
  12. 12.98 − 29 =
  13. 13.41 + 9 =
  14. 14.44 − 29 =
  15. 15.511 + 99 =
  16. 16.215 − 99 =
  17. 17.190 + 99 =
  18. 18.84 − 29 =
  19. 19.96 − 29 =
  20. 20.29 + 9 =
  21. 21.30 + 19 =
  22. 22.32 + 9 =
  23. 23.66 + 9 =
  24. 24.46 + 9 =
  25. 25.44 + 29 =
  26. 26.22 + 19 =
  27. 27.48 + 9 =
  28. 28.67 + 29 =
  29. 29.47 + 19 =
  30. 30.16 − 9 =
  31. 31.54 + 29 =
  32. 32.70 − 19 =
  33. 33.77 + 29 =
  34. 34.54 + 19 =
  35. 35.579 + 99 =
  36. 36.306 + 99 =
  37. 37.82 − 9 =
  38. 38.15 − 9 =
  39. 39.63 + 19 =
  40. 40.61 + 29 =

Answer key

  1. 29
  2. 72
  3. 14
  4. 344
  5. 21
  6. 90
  7. 8
  8. 80
  9. 30
  10. 53
  11. 350
  12. 69
  13. 50
  14. 15
  15. 610
  16. 116
  17. 289
  18. 55
  19. 67
  20. 38
  21. 49
  22. 41
  23. 75
  24. 55
  25. 73
  26. 41
  27. 57
  28. 96
  29. 66
  30. 7
  31. 83
  32. 51
  33. 106
  34. 73
  35. 678
  36. 405
  37. 73
  38. 6
  39. 82
  40. 90

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