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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 309 · 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. 1.118 + 99 =
  2. 2.750 − 99 =
  3. 3.43 − 19 =
  4. 4.47 + 29 =
  5. 5.104 − 29 =
  6. 6.346 − 99 =
  7. 7.286 − 99 =
  8. 8.615 − 99 =
  9. 9.80 + 19 =
  10. 10.13 + 9 =
  11. 11.53 + 19 =
  12. 12.13 + 19 =
  13. 13.88 − 9 =
  14. 14.78 + 19 =
  15. 15.702 − 99 =
  16. 16.15 + 19 =
  17. 17.459 − 99 =
  18. 18.665 − 99 =
  19. 19.57 − 19 =
  20. 20.108 − 29 =
  21. 21.63 − 9 =
  22. 22.385 + 99 =
  23. 23.61 + 9 =
  24. 24.36 − 19 =
  25. 25.44 + 9 =
  26. 26.32 + 19 =
  27. 27.195 + 99 =
  28. 28.65 + 29 =
  29. 29.57 + 29 =
  30. 30.65 + 9 =
  31. 31.23 + 19 =
  32. 32.28 + 19 =
  33. 33.226 + 99 =
  34. 34.39 − 19 =
  35. 35.503 − 99 =
  36. 36.74 − 9 =
  37. 37.73 − 29 =
  38. 38.55 − 9 =
  39. 39.21 − 9 =
  40. 40.17 + 29 =

Answer key

  1. 217
  2. 651
  3. 24
  4. 76
  5. 75
  6. 247
  7. 187
  8. 516
  9. 99
  10. 22
  11. 72
  12. 32
  13. 79
  14. 97
  15. 603
  16. 34
  17. 360
  18. 566
  19. 38
  20. 79
  21. 54
  22. 484
  23. 70
  24. 17
  25. 53
  26. 51
  27. 294
  28. 94
  29. 86
  30. 74
  31. 42
  32. 47
  33. 325
  34. 20
  35. 404
  36. 65
  37. 44
  38. 46
  39. 12
  40. 46

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