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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 634 · 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. 1.538 + 99 =
  2. 2.22 + 19 =
  3. 3.42 − 19 =
  4. 4.79 + 19 =
  5. 5.157 + 99 =
  6. 6.282 − 99 =
  7. 7.496 + 99 =
  8. 8.85 − 29 =
  9. 9.46 + 9 =
  10. 10.71 − 29 =
  11. 11.233 + 99 =
  12. 12.31 − 19 =
  13. 13.322 + 99 =
  14. 14.74 − 29 =
  15. 15.25 + 9 =
  16. 16.105 − 29 =
  17. 17.37 + 19 =
  18. 18.12 + 9 =
  19. 19.34 + 29 =
  20. 20.73 + 29 =
  21. 21.267 − 99 =
  22. 22.408 + 99 =
  23. 23.687 − 99 =
  24. 24.79 − 19 =
  25. 25.32 + 9 =
  26. 26.234 − 99 =
  27. 27.359 + 99 =
  28. 28.18 + 29 =
  29. 29.65 + 9 =
  30. 30.53 + 19 =
  31. 31.377 + 99 =
  32. 32.242 + 99 =
  33. 33.49 − 29 =
  34. 34.98 − 29 =
  35. 35.75 + 9 =
  36. 36.69 + 19 =
  37. 37.63 + 19 =
  38. 38.473 + 99 =
  39. 39.30 + 9 =
  40. 40.30 − 9 =

Answer key

  1. 637
  2. 41
  3. 23
  4. 98
  5. 256
  6. 183
  7. 595
  8. 56
  9. 55
  10. 42
  11. 332
  12. 12
  13. 421
  14. 45
  15. 34
  16. 76
  17. 56
  18. 21
  19. 63
  20. 102
  21. 168
  22. 507
  23. 588
  24. 60
  25. 41
  26. 135
  27. 458
  28. 47
  29. 74
  30. 72
  31. 476
  32. 341
  33. 20
  34. 69
  35. 84
  36. 88
  37. 82
  38. 572
  39. 39
  40. 21

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