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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 920 · 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. 1.80 + 19 =
  2. 2.60 − 9 =
  3. 3.360 − 99 =
  4. 4.34 − 9 =
  5. 5.103 − 29 =
  6. 6.88 − 9 =
  7. 7.48 − 29 =
  8. 8.63 + 29 =
  9. 9.24 + 9 =
  10. 10.57 − 29 =
  11. 11.28 + 19 =
  12. 12.23 − 19 =
  13. 13.62 − 9 =
  14. 14.80 + 9 =
  15. 15.70 − 29 =
  16. 16.534 + 99 =
  17. 17.41 − 29 =
  18. 18.429 − 99 =
  19. 19.16 + 29 =
  20. 20.26 + 19 =
  21. 21.59 − 29 =
  22. 22.184 − 99 =
  23. 23.47 + 19 =
  24. 24.80 + 29 =
  25. 25.83 − 9 =
  26. 26.51 − 19 =
  27. 27.34 − 19 =
  28. 28.12 + 9 =
  29. 29.46 − 29 =
  30. 30.86 − 9 =
  31. 31.873 − 99 =
  32. 32.749 − 99 =
  33. 33.87 − 9 =
  34. 34.224 − 99 =
  35. 35.689 − 99 =
  36. 36.29 + 19 =
  37. 37.43 − 9 =
  38. 38.78 + 9 =
  39. 39.663 − 99 =
  40. 40.68 + 19 =

Answer key

  1. 99
  2. 51
  3. 261
  4. 25
  5. 74
  6. 79
  7. 19
  8. 92
  9. 33
  10. 28
  11. 47
  12. 4
  13. 53
  14. 89
  15. 41
  16. 633
  17. 12
  18. 330
  19. 45
  20. 45
  21. 30
  22. 85
  23. 66
  24. 109
  25. 74
  26. 32
  27. 15
  28. 21
  29. 17
  30. 77
  31. 774
  32. 650
  33. 78
  34. 125
  35. 590
  36. 48
  37. 34
  38. 87
  39. 564
  40. 87

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