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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 711 · 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. 1.39 + 29 =
  2. 2.855 − 99 =
  3. 3.70 − 19 =
  4. 4.79 + 9 =
  5. 5.17 + 29 =
  6. 6.345 + 99 =
  7. 7.20 − 9 =
  8. 8.77 − 29 =
  9. 9.46 + 9 =
  10. 10.624 + 99 =
  11. 11.34 + 9 =
  12. 12.58 + 29 =
  13. 13.15 − 9 =
  14. 14.37 + 9 =
  15. 15.670 + 99 =
  16. 16.25 − 9 =
  17. 17.49 − 9 =
  18. 18.57 + 19 =
  19. 19.32 + 29 =
  20. 20.497 + 99 =
  21. 21.69 + 19 =
  22. 22.687 − 99 =
  23. 23.334 + 99 =
  24. 24.32 + 9 =
  25. 25.207 + 99 =
  26. 26.61 + 9 =
  27. 27.90 − 19 =
  28. 28.52 + 19 =
  29. 29.883 − 99 =
  30. 30.765 − 99 =
  31. 31.77 − 9 =
  32. 32.63 + 9 =
  33. 33.76 − 9 =
  34. 34.329 − 99 =
  35. 35.732 − 99 =
  36. 36.59 − 29 =
  37. 37.86 − 9 =
  38. 38.844 − 99 =
  39. 39.48 − 9 =
  40. 40.179 − 99 =

Answer key

  1. 68
  2. 756
  3. 51
  4. 88
  5. 46
  6. 444
  7. 11
  8. 48
  9. 55
  10. 723
  11. 43
  12. 87
  13. 6
  14. 46
  15. 769
  16. 16
  17. 40
  18. 76
  19. 61
  20. 596
  21. 88
  22. 588
  23. 433
  24. 41
  25. 306
  26. 70
  27. 71
  28. 71
  29. 784
  30. 666
  31. 68
  32. 72
  33. 67
  34. 230
  35. 633
  36. 30
  37. 77
  38. 745
  39. 39
  40. 80

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