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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 5 · 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. 1.712 + 99 =
  2. 2.635 − 99 =
  3. 3.54 − 29 =
  4. 4.153 + 99 =
  5. 5.79 + 9 =
  6. 6.39 − 9 =
  7. 7.54 + 29 =
  8. 8.66 + 9 =
  9. 9.51 − 29 =
  10. 10.46 + 9 =
  11. 11.63 − 29 =
  12. 12.176 + 99 =
  13. 13.69 − 19 =
  14. 14.53 + 9 =
  15. 15.26 + 29 =
  16. 16.369 − 99 =
  17. 17.24 − 9 =
  18. 18.182 − 99 =
  19. 19.251 + 99 =
  20. 20.42 + 19 =
  21. 21.29 + 9 =
  22. 22.77 + 29 =
  23. 23.56 − 9 =
  24. 24.37 − 9 =
  25. 25.58 − 29 =
  26. 26.26 + 9 =
  27. 27.30 + 19 =
  28. 28.57 − 29 =
  29. 29.45 + 19 =
  30. 30.93 − 19 =
  31. 31.51 + 29 =
  32. 32.64 + 19 =
  33. 33.783 + 99 =
  34. 34.630 − 99 =
  35. 35.511 + 99 =
  36. 36.46 + 29 =
  37. 37.50 − 9 =
  38. 38.44 − 9 =
  39. 39.503 − 99 =
  40. 40.512 − 99 =

Answer key

  1. 811
  2. 536
  3. 25
  4. 252
  5. 88
  6. 30
  7. 83
  8. 75
  9. 22
  10. 55
  11. 34
  12. 275
  13. 50
  14. 62
  15. 55
  16. 270
  17. 15
  18. 83
  19. 350
  20. 61
  21. 38
  22. 106
  23. 47
  24. 28
  25. 29
  26. 35
  27. 49
  28. 28
  29. 64
  30. 74
  31. 80
  32. 83
  33. 882
  34. 531
  35. 610
  36. 75
  37. 41
  38. 35
  39. 404
  40. 413

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