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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 669 · 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. 1.410 − 99 =
  2. 2.108 − 29 =
  3. 3.651 + 99 =
  4. 4.763 + 99 =
  5. 5.281 + 99 =
  6. 6.52 − 9 =
  7. 7.34 + 9 =
  8. 8.551 + 99 =
  9. 9.55 − 19 =
  10. 10.79 + 19 =
  11. 11.78 + 19 =
  12. 12.57 − 19 =
  13. 13.171 − 99 =
  14. 14.701 + 99 =
  15. 15.190 + 99 =
  16. 16.49 − 29 =
  17. 17.401 + 99 =
  18. 18.659 − 99 =
  19. 19.324 − 99 =
  20. 20.849 − 99 =
  21. 21.25 + 29 =
  22. 22.70 − 19 =
  23. 23.50 + 29 =
  24. 24.395 + 99 =
  25. 25.79 + 9 =
  26. 26.80 + 29 =
  27. 27.66 − 29 =
  28. 28.721 − 99 =
  29. 29.42 + 9 =
  30. 30.16 + 19 =
  31. 31.29 + 9 =
  32. 32.29 + 19 =
  33. 33.20 − 9 =
  34. 34.78 − 29 =
  35. 35.58 − 9 =
  36. 36.12 − 9 =
  37. 37.34 − 29 =
  38. 38.815 − 99 =
  39. 39.32 + 19 =
  40. 40.44 + 9 =

Answer key

  1. 311
  2. 79
  3. 750
  4. 862
  5. 380
  6. 43
  7. 43
  8. 650
  9. 36
  10. 98
  11. 97
  12. 38
  13. 72
  14. 800
  15. 289
  16. 20
  17. 500
  18. 560
  19. 225
  20. 750
  21. 54
  22. 51
  23. 79
  24. 494
  25. 88
  26. 109
  27. 37
  28. 622
  29. 51
  30. 35
  31. 38
  32. 48
  33. 11
  34. 49
  35. 49
  36. 3
  37. 5
  38. 716
  39. 51
  40. 53

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