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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 753 · 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. 1.29 + 29 =
  2. 2.64 − 9 =
  3. 3.456 + 99 =
  4. 4.31 + 19 =
  5. 5.68 + 19 =
  6. 6.228 − 99 =
  7. 7.736 − 99 =
  8. 8.69 + 19 =
  9. 9.67 − 9 =
  10. 10.42 + 9 =
  11. 11.267 − 99 =
  12. 12.721 − 99 =
  13. 13.290 + 99 =
  14. 14.42 − 19 =
  15. 15.49 − 19 =
  16. 16.622 + 99 =
  17. 17.20 − 9 =
  18. 18.30 − 9 =
  19. 19.75 − 9 =
  20. 20.32 − 9 =
  21. 21.82 − 19 =
  22. 22.40 − 29 =
  23. 23.761 − 99 =
  24. 24.69 − 19 =
  25. 25.64 − 29 =
  26. 26.51 + 29 =
  27. 27.28 − 19 =
  28. 28.19 + 19 =
  29. 29.46 + 9 =
  30. 30.47 + 9 =
  31. 31.79 − 19 =
  32. 32.94 − 29 =
  33. 33.25 + 19 =
  34. 34.800 + 99 =
  35. 35.38 + 9 =
  36. 36.762 − 99 =
  37. 37.73 + 19 =
  38. 38.47 − 29 =
  39. 39.478 − 99 =
  40. 40.72 − 9 =

Answer key

  1. 58
  2. 55
  3. 555
  4. 50
  5. 87
  6. 129
  7. 637
  8. 88
  9. 58
  10. 51
  11. 168
  12. 622
  13. 389
  14. 23
  15. 30
  16. 721
  17. 11
  18. 21
  19. 66
  20. 23
  21. 63
  22. 11
  23. 662
  24. 50
  25. 35
  26. 80
  27. 9
  28. 38
  29. 55
  30. 56
  31. 60
  32. 65
  33. 44
  34. 899
  35. 47
  36. 663
  37. 92
  38. 18
  39. 379
  40. 63

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