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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 767 · 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. 1.716 + 99 =
  2. 2.42 − 19 =
  3. 3.533 + 99 =
  4. 4.788 − 99 =
  5. 5.65 + 19 =
  6. 6.78 + 19 =
  7. 7.22 + 19 =
  8. 8.84 − 29 =
  9. 9.13 − 9 =
  10. 10.46 + 29 =
  11. 11.37 + 29 =
  12. 12.777 + 99 =
  13. 13.38 + 19 =
  14. 14.75 − 19 =
  15. 15.12 + 9 =
  16. 16.68 + 9 =
  17. 17.291 + 99 =
  18. 18.31 − 19 =
  19. 19.71 + 19 =
  20. 20.70 − 29 =
  21. 21.31 + 9 =
  22. 22.16 + 19 =
  23. 23.425 + 99 =
  24. 24.50 + 9 =
  25. 25.75 − 9 =
  26. 26.26 − 19 =
  27. 27.70 + 29 =
  28. 28.798 + 99 =
  29. 29.58 − 9 =
  30. 30.33 + 29 =
  31. 31.613 + 99 =
  32. 32.222 + 99 =
  33. 33.38 + 29 =
  34. 34.279 − 99 =
  35. 35.192 − 99 =
  36. 36.31 − 9 =
  37. 37.724 − 99 =
  38. 38.76 + 29 =
  39. 39.52 − 19 =
  40. 40.27 − 19 =

Answer key

  1. 815
  2. 23
  3. 632
  4. 689
  5. 84
  6. 97
  7. 41
  8. 55
  9. 4
  10. 75
  11. 66
  12. 876
  13. 57
  14. 56
  15. 21
  16. 77
  17. 390
  18. 12
  19. 90
  20. 41
  21. 40
  22. 35
  23. 524
  24. 59
  25. 66
  26. 7
  27. 99
  28. 897
  29. 49
  30. 62
  31. 712
  32. 321
  33. 67
  34. 180
  35. 93
  36. 22
  37. 625
  38. 105
  39. 33
  40. 8

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