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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 45 · 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. 1.406 − 99 =
  2. 2.303 + 99 =
  3. 3.303 − 99 =
  4. 4.41 + 9 =
  5. 5.76 − 9 =
  6. 6.779 + 99 =
  7. 7.45 − 19 =
  8. 8.59 − 9 =
  9. 9.19 + 19 =
  10. 10.305 + 99 =
  11. 11.30 + 9 =
  12. 12.70 + 9 =
  13. 13.24 − 9 =
  14. 14.98 − 19 =
  15. 15.239 − 99 =
  16. 16.42 − 29 =
  17. 17.50 − 9 =
  18. 18.18 + 19 =
  19. 19.76 − 19 =
  20. 20.78 − 19 =
  21. 21.38 + 29 =
  22. 22.73 + 9 =
  23. 23.76 + 19 =
  24. 24.22 + 19 =
  25. 25.48 − 19 =
  26. 26.52 + 9 =
  27. 27.70 − 29 =
  28. 28.64 + 9 =
  29. 29.27 + 9 =
  30. 30.381 − 99 =
  31. 31.62 − 19 =
  32. 32.64 − 29 =
  33. 33.157 + 99 =
  34. 34.717 − 99 =
  35. 35.465 + 99 =
  36. 36.70 + 19 =
  37. 37.18 − 9 =
  38. 38.60 − 29 =
  39. 39.16 − 9 =
  40. 40.709 + 99 =

Answer key

  1. 307
  2. 402
  3. 204
  4. 50
  5. 67
  6. 878
  7. 26
  8. 50
  9. 38
  10. 404
  11. 39
  12. 79
  13. 15
  14. 79
  15. 140
  16. 13
  17. 41
  18. 37
  19. 57
  20. 59
  21. 67
  22. 82
  23. 95
  24. 41
  25. 29
  26. 61
  27. 41
  28. 73
  29. 36
  30. 282
  31. 43
  32. 35
  33. 256
  34. 618
  35. 564
  36. 89
  37. 9
  38. 31
  39. 7
  40. 808

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