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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 672 · 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. 1.369 − 99 =
  2. 2.385 − 99 =
  3. 3.188 + 99 =
  4. 4.19 + 29 =
  5. 5.55 − 9 =
  6. 6.46 + 29 =
  7. 7.13 − 9 =
  8. 8.12 + 29 =
  9. 9.35 + 19 =
  10. 10.33 + 29 =
  11. 11.69 − 19 =
  12. 12.493 − 99 =
  13. 13.14 − 9 =
  14. 14.63 − 19 =
  15. 15.276 − 99 =
  16. 16.24 − 9 =
  17. 17.79 − 19 =
  18. 18.630 + 99 =
  19. 19.69 + 9 =
  20. 20.57 + 19 =
  21. 21.58 − 29 =
  22. 22.58 − 9 =
  23. 23.466 + 99 =
  24. 24.88 − 9 =
  25. 25.46 − 9 =
  26. 26.246 + 99 =
  27. 27.365 + 99 =
  28. 28.92 − 29 =
  29. 29.143 + 99 =
  30. 30.69 + 29 =
  31. 31.894 − 99 =
  32. 32.31 + 29 =
  33. 33.181 − 99 =
  34. 34.536 − 99 =
  35. 35.14 + 9 =
  36. 36.37 + 9 =
  37. 37.50 + 29 =
  38. 38.243 − 99 =
  39. 39.59 − 19 =
  40. 40.706 + 99 =

Answer key

  1. 270
  2. 286
  3. 287
  4. 48
  5. 46
  6. 75
  7. 4
  8. 41
  9. 54
  10. 62
  11. 50
  12. 394
  13. 5
  14. 44
  15. 177
  16. 15
  17. 60
  18. 729
  19. 78
  20. 76
  21. 29
  22. 49
  23. 565
  24. 79
  25. 37
  26. 345
  27. 464
  28. 63
  29. 242
  30. 98
  31. 795
  32. 60
  33. 82
  34. 437
  35. 23
  36. 46
  37. 79
  38. 144
  39. 40
  40. 805

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