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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 405 · 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. 1.311 + 99 =
  2. 2.66 − 9 =
  3. 3.125 + 99 =
  4. 4.46 − 29 =
  5. 5.29 + 9 =
  6. 6.51 − 29 =
  7. 7.49 − 19 =
  8. 8.56 − 9 =
  9. 9.22 + 29 =
  10. 10.14 + 19 =
  11. 11.32 + 29 =
  12. 12.691 − 99 =
  13. 13.18 + 19 =
  14. 14.78 − 19 =
  15. 15.24 + 9 =
  16. 16.39 + 19 =
  17. 17.65 − 19 =
  18. 18.58 − 19 =
  19. 19.281 + 99 =
  20. 20.89 − 29 =
  21. 21.76 − 29 =
  22. 22.222 + 99 =
  23. 23.155 + 99 =
  24. 24.43 − 19 =
  25. 25.340 + 99 =
  26. 26.536 + 99 =
  27. 27.186 − 99 =
  28. 28.24 + 29 =
  29. 29.612 − 99 =
  30. 30.54 − 29 =
  31. 31.563 + 99 =
  32. 32.345 + 99 =
  33. 33.40 + 19 =
  34. 34.69 + 29 =
  35. 35.270 − 99 =
  36. 36.63 + 29 =
  37. 37.78 + 9 =
  38. 38.650 + 99 =
  39. 39.50 + 19 =
  40. 40.65 + 9 =

Answer key

  1. 410
  2. 57
  3. 224
  4. 17
  5. 38
  6. 22
  7. 30
  8. 47
  9. 51
  10. 33
  11. 61
  12. 592
  13. 37
  14. 59
  15. 33
  16. 58
  17. 46
  18. 39
  19. 380
  20. 60
  21. 47
  22. 321
  23. 254
  24. 24
  25. 439
  26. 635
  27. 87
  28. 53
  29. 513
  30. 25
  31. 662
  32. 444
  33. 59
  34. 98
  35. 171
  36. 92
  37. 87
  38. 749
  39. 69
  40. 74

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