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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 21 · 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. 1.755 + 99 =
  2. 2.65 + 9 =
  3. 3.88 − 9 =
  4. 4.26 + 29 =
  5. 5.33 − 19 =
  6. 6.83 − 9 =
  7. 7.23 + 9 =
  8. 8.14 + 19 =
  9. 9.40 + 29 =
  10. 10.394 + 99 =
  11. 11.15 + 29 =
  12. 12.36 − 9 =
  13. 13.70 + 9 =
  14. 14.35 + 9 =
  15. 15.77 + 9 =
  16. 16.67 + 9 =
  17. 17.496 − 99 =
  18. 18.311 + 99 =
  19. 19.19 + 29 =
  20. 20.38 − 29 =
  21. 21.26 + 19 =
  22. 22.283 + 99 =
  23. 23.51 − 29 =
  24. 24.52 − 19 =
  25. 25.80 + 9 =
  26. 26.49 + 29 =
  27. 27.853 − 99 =
  28. 28.31 + 9 =
  29. 29.48 − 9 =
  30. 30.401 + 99 =
  31. 31.715 − 99 =
  32. 32.22 + 9 =
  33. 33.40 − 9 =
  34. 34.383 + 99 =
  35. 35.43 + 29 =
  36. 36.24 − 19 =
  37. 37.76 − 29 =
  38. 38.68 − 19 =
  39. 39.43 + 9 =
  40. 40.31 − 9 =

Answer key

  1. 854
  2. 74
  3. 79
  4. 55
  5. 14
  6. 74
  7. 32
  8. 33
  9. 69
  10. 493
  11. 44
  12. 27
  13. 79
  14. 44
  15. 86
  16. 76
  17. 397
  18. 410
  19. 48
  20. 9
  21. 45
  22. 382
  23. 22
  24. 33
  25. 89
  26. 78
  27. 754
  28. 40
  29. 39
  30. 500
  31. 616
  32. 31
  33. 31
  34. 482
  35. 72
  36. 5
  37. 47
  38. 49
  39. 52
  40. 22

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