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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 678 · 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. 1.53 − 9 =
  2. 2.25 + 9 =
  3. 3.666 − 99 =
  4. 4.62 + 9 =
  5. 5.47 − 19 =
  6. 6.186 + 99 =
  7. 7.76 + 29 =
  8. 8.50 + 9 =
  9. 9.39 − 9 =
  10. 10.26 + 29 =
  11. 11.268 − 99 =
  12. 12.327 − 99 =
  13. 13.83 − 9 =
  14. 14.230 − 99 =
  15. 15.87 − 29 =
  16. 16.70 + 19 =
  17. 17.453 − 99 =
  18. 18.28 + 19 =
  19. 19.42 + 9 =
  20. 20.560 − 99 =
  21. 21.446 + 99 =
  22. 22.504 − 99 =
  23. 23.753 + 99 =
  24. 24.45 + 9 =
  25. 25.24 − 19 =
  26. 26.49 − 9 =
  27. 27.81 − 19 =
  28. 28.70 − 29 =
  29. 29.17 + 19 =
  30. 30.47 − 9 =
  31. 31.39 + 19 =
  32. 32.64 − 29 =
  33. 33.49 + 9 =
  34. 34.64 + 29 =
  35. 35.21 + 29 =
  36. 36.399 − 99 =
  37. 37.602 + 99 =
  38. 38.527 + 99 =
  39. 39.86 − 9 =
  40. 40.56 + 19 =

Answer key

  1. 44
  2. 34
  3. 567
  4. 71
  5. 28
  6. 285
  7. 105
  8. 59
  9. 30
  10. 55
  11. 169
  12. 228
  13. 74
  14. 131
  15. 58
  16. 89
  17. 354
  18. 47
  19. 51
  20. 461
  21. 545
  22. 405
  23. 852
  24. 54
  25. 5
  26. 40
  27. 62
  28. 41
  29. 36
  30. 38
  31. 58
  32. 35
  33. 58
  34. 93
  35. 50
  36. 300
  37. 701
  38. 626
  39. 77
  40. 75

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