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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 232 · 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. 1.354 + 99 =
  2. 2.200 − 99 =
  3. 3.24 − 9 =
  4. 4.41 − 29 =
  5. 5.756 − 99 =
  6. 6.51 − 19 =
  7. 7.52 − 19 =
  8. 8.97 − 19 =
  9. 9.27 + 9 =
  10. 10.869 − 99 =
  11. 11.104 − 29 =
  12. 12.16 + 29 =
  13. 13.65 − 29 =
  14. 14.221 + 99 =
  15. 15.81 − 9 =
  16. 16.496 + 99 =
  17. 17.39 − 9 =
  18. 18.38 + 29 =
  19. 19.63 + 9 =
  20. 20.665 + 99 =
  21. 21.158 − 99 =
  22. 22.81 − 29 =
  23. 23.46 − 19 =
  24. 24.80 + 9 =
  25. 25.19 − 9 =
  26. 26.42 − 9 =
  27. 27.143 + 99 =
  28. 28.47 − 19 =
  29. 29.65 + 9 =
  30. 30.89 − 9 =
  31. 31.33 + 9 =
  32. 32.59 + 19 =
  33. 33.28 + 9 =
  34. 34.284 − 99 =
  35. 35.50 − 29 =
  36. 36.87 − 9 =
  37. 37.166 + 99 =
  38. 38.56 + 9 =
  39. 39.30 + 29 =
  40. 40.624 + 99 =

Answer key

  1. 453
  2. 101
  3. 15
  4. 12
  5. 657
  6. 32
  7. 33
  8. 78
  9. 36
  10. 770
  11. 75
  12. 45
  13. 36
  14. 320
  15. 72
  16. 595
  17. 30
  18. 67
  19. 72
  20. 764
  21. 59
  22. 52
  23. 27
  24. 89
  25. 10
  26. 33
  27. 242
  28. 28
  29. 74
  30. 80
  31. 42
  32. 78
  33. 37
  34. 185
  35. 21
  36. 78
  37. 265
  38. 65
  39. 59
  40. 723

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