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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 679 · 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. 1.378 − 99 =
  2. 2.65 − 29 =
  3. 3.91 − 19 =
  4. 4.13 + 29 =
  5. 5.42 − 19 =
  6. 6.37 + 9 =
  7. 7.42 + 19 =
  8. 8.16 + 19 =
  9. 9.41 + 19 =
  10. 10.47 + 19 =
  11. 11.42 − 29 =
  12. 12.501 − 99 =
  13. 13.39 + 19 =
  14. 14.72 + 29 =
  15. 15.35 + 19 =
  16. 16.411 + 99 =
  17. 17.45 + 9 =
  18. 18.64 + 19 =
  19. 19.29 + 9 =
  20. 20.79 − 19 =
  21. 21.54 − 9 =
  22. 22.789 + 99 =
  23. 23.50 + 19 =
  24. 24.380 + 99 =
  25. 25.34 + 19 =
  26. 26.82 − 19 =
  27. 27.80 − 19 =
  28. 28.406 − 99 =
  29. 29.818 − 99 =
  30. 30.565 − 99 =
  31. 31.72 + 9 =
  32. 32.32 + 29 =
  33. 33.233 + 99 =
  34. 34.77 − 29 =
  35. 35.66 + 9 =
  36. 36.223 − 99 =
  37. 37.28 + 19 =
  38. 38.67 − 19 =
  39. 39.59 − 19 =
  40. 40.21 + 9 =

Answer key

  1. 279
  2. 36
  3. 72
  4. 42
  5. 23
  6. 46
  7. 61
  8. 35
  9. 60
  10. 66
  11. 13
  12. 402
  13. 58
  14. 101
  15. 54
  16. 510
  17. 54
  18. 83
  19. 38
  20. 60
  21. 45
  22. 888
  23. 69
  24. 479
  25. 53
  26. 63
  27. 61
  28. 307
  29. 719
  30. 466
  31. 81
  32. 61
  33. 332
  34. 48
  35. 75
  36. 124
  37. 47
  38. 48
  39. 40
  40. 30

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