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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 123 · 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. 1.69 − 29 =
  2. 2.425 + 99 =
  3. 3.578 − 99 =
  4. 4.367 + 99 =
  5. 5.692 − 99 =
  6. 6.29 + 9 =
  7. 7.57 − 29 =
  8. 8.47 − 9 =
  9. 9.64 + 19 =
  10. 10.73 + 29 =
  11. 11.67 − 29 =
  12. 12.28 − 9 =
  13. 13.12 + 19 =
  14. 14.39 + 29 =
  15. 15.43 − 29 =
  16. 16.76 − 29 =
  17. 17.31 + 29 =
  18. 18.85 − 19 =
  19. 19.86 − 9 =
  20. 20.347 − 99 =
  21. 21.37 + 9 =
  22. 22.98 − 19 =
  23. 23.75 + 9 =
  24. 24.76 + 9 =
  25. 25.509 − 99 =
  26. 26.20 + 9 =
  27. 27.370 − 99 =
  28. 28.82 − 19 =
  29. 29.43 + 9 =
  30. 30.62 + 19 =
  31. 31.15 + 9 =
  32. 32.73 + 19 =
  33. 33.230 − 99 =
  34. 34.685 + 99 =
  35. 35.63 − 9 =
  36. 36.67 + 9 =
  37. 37.45 − 19 =
  38. 38.55 − 29 =
  39. 39.13 + 9 =
  40. 40.34 − 29 =

Answer key

  1. 40
  2. 524
  3. 479
  4. 466
  5. 593
  6. 38
  7. 28
  8. 38
  9. 83
  10. 102
  11. 38
  12. 19
  13. 31
  14. 68
  15. 14
  16. 47
  17. 60
  18. 66
  19. 77
  20. 248
  21. 46
  22. 79
  23. 84
  24. 85
  25. 410
  26. 29
  27. 271
  28. 63
  29. 52
  30. 81
  31. 24
  32. 92
  33. 131
  34. 784
  35. 54
  36. 76
  37. 26
  38. 26
  39. 22
  40. 5

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