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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 223 · 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. 1.213 + 99 =
  2. 2.60 + 9 =
  3. 3.69 − 9 =
  4. 4.340 − 99 =
  5. 5.315 − 99 =
  6. 6.708 + 99 =
  7. 7.64 + 9 =
  8. 8.37 + 9 =
  9. 9.82 − 19 =
  10. 10.79 + 29 =
  11. 11.850 − 99 =
  12. 12.90 − 19 =
  13. 13.77 + 29 =
  14. 14.31 + 9 =
  15. 15.534 − 99 =
  16. 16.724 + 99 =
  17. 17.43 − 29 =
  18. 18.639 + 99 =
  19. 19.646 − 99 =
  20. 20.80 − 29 =
  21. 21.379 − 99 =
  22. 22.535 + 99 =
  23. 23.73 − 29 =
  24. 24.107 − 29 =
  25. 25.95 − 29 =
  26. 26.592 − 99 =
  27. 27.31 + 29 =
  28. 28.103 − 29 =
  29. 29.60 − 19 =
  30. 30.23 − 9 =
  31. 31.99 − 29 =
  32. 32.35 + 29 =
  33. 33.45 − 19 =
  34. 34.549 + 99 =
  35. 35.28 + 29 =
  36. 36.31 − 19 =
  37. 37.22 + 9 =
  38. 38.38 − 19 =
  39. 39.37 − 29 =
  40. 40.328 + 99 =

Answer key

  1. 312
  2. 69
  3. 60
  4. 241
  5. 216
  6. 807
  7. 73
  8. 46
  9. 63
  10. 108
  11. 751
  12. 71
  13. 106
  14. 40
  15. 435
  16. 823
  17. 14
  18. 738
  19. 547
  20. 51
  21. 280
  22. 634
  23. 44
  24. 78
  25. 66
  26. 493
  27. 60
  28. 74
  29. 41
  30. 14
  31. 70
  32. 64
  33. 26
  34. 648
  35. 57
  36. 12
  37. 31
  38. 19
  39. 8
  40. 427

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