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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 215 · 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. 1.356 − 99 =
  2. 2.35 + 29 =
  3. 3.64 + 9 =
  4. 4.32 − 9 =
  5. 5.273 − 99 =
  6. 6.15 − 9 =
  7. 7.47 + 9 =
  8. 8.46 + 29 =
  9. 9.226 − 99 =
  10. 10.209 − 99 =
  11. 11.570 + 99 =
  12. 12.49 − 29 =
  13. 13.100 − 29 =
  14. 14.386 + 99 =
  15. 15.630 + 99 =
  16. 16.23 − 9 =
  17. 17.46 + 19 =
  18. 18.277 + 99 =
  19. 19.63 + 29 =
  20. 20.79 + 9 =
  21. 21.604 + 99 =
  22. 22.856 − 99 =
  23. 23.605 + 99 =
  24. 24.41 + 9 =
  25. 25.67 − 29 =
  26. 26.73 + 19 =
  27. 27.63 − 19 =
  28. 28.82 − 9 =
  29. 29.83 − 29 =
  30. 30.35 + 9 =
  31. 31.49 + 9 =
  32. 32.29 + 9 =
  33. 33.54 + 19 =
  34. 34.28 + 19 =
  35. 35.12 − 9 =
  36. 36.54 + 9 =
  37. 37.89 − 9 =
  38. 38.85 − 9 =
  39. 39.23 + 19 =
  40. 40.38 + 29 =

Answer key

  1. 257
  2. 64
  3. 73
  4. 23
  5. 174
  6. 6
  7. 56
  8. 75
  9. 127
  10. 110
  11. 669
  12. 20
  13. 71
  14. 485
  15. 729
  16. 14
  17. 65
  18. 376
  19. 92
  20. 88
  21. 703
  22. 757
  23. 704
  24. 50
  25. 38
  26. 92
  27. 44
  28. 73
  29. 54
  30. 44
  31. 58
  32. 38
  33. 73
  34. 47
  35. 3
  36. 63
  37. 80
  38. 76
  39. 42
  40. 67

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