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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 917 · 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. 1.56 + 29 =
  2. 2.109 − 29 =
  3. 3.39 + 29 =
  4. 4.308 + 99 =
  5. 5.27 + 9 =
  6. 6.69 + 9 =
  7. 7.29 − 9 =
  8. 8.787 + 99 =
  9. 9.212 + 99 =
  10. 10.39 + 19 =
  11. 11.45 + 9 =
  12. 12.75 − 19 =
  13. 13.43 − 29 =
  14. 14.51 + 9 =
  15. 15.61 − 9 =
  16. 16.17 + 29 =
  17. 17.61 − 29 =
  18. 18.64 − 9 =
  19. 19.778 − 99 =
  20. 20.473 + 99 =
  21. 21.153 − 99 =
  22. 22.57 + 9 =
  23. 23.404 − 99 =
  24. 24.57 − 9 =
  25. 25.880 − 99 =
  26. 26.551 + 99 =
  27. 27.29 + 9 =
  28. 28.26 + 9 =
  29. 29.40 + 9 =
  30. 30.68 + 29 =
  31. 31.22 + 29 =
  32. 32.24 + 19 =
  33. 33.28 − 19 =
  34. 34.41 − 9 =
  35. 35.90 − 29 =
  36. 36.37 + 9 =
  37. 37.23 − 9 =
  38. 38.58 − 29 =
  39. 39.849 − 99 =
  40. 40.416 − 99 =

Answer key

  1. 85
  2. 80
  3. 68
  4. 407
  5. 36
  6. 78
  7. 20
  8. 886
  9. 311
  10. 58
  11. 54
  12. 56
  13. 14
  14. 60
  15. 52
  16. 46
  17. 32
  18. 55
  19. 679
  20. 572
  21. 54
  22. 66
  23. 305
  24. 48
  25. 781
  26. 650
  27. 38
  28. 35
  29. 49
  30. 97
  31. 51
  32. 43
  33. 9
  34. 32
  35. 61
  36. 46
  37. 14
  38. 29
  39. 750
  40. 317

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