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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 302 · 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. 1.521 + 99 =
  2. 2.218 − 99 =
  3. 3.44 + 9 =
  4. 4.73 + 9 =
  5. 5.99 − 29 =
  6. 6.60 − 9 =
  7. 7.538 + 99 =
  8. 8.31 + 29 =
  9. 9.42 + 19 =
  10. 10.88 − 29 =
  11. 11.63 + 19 =
  12. 12.709 − 99 =
  13. 13.57 + 19 =
  14. 14.78 + 19 =
  15. 15.79 + 19 =
  16. 16.31 + 19 =
  17. 17.36 + 19 =
  18. 18.749 − 99 =
  19. 19.23 + 29 =
  20. 20.249 − 99 =
  21. 21.30 + 9 =
  22. 22.371 + 99 =
  23. 23.58 + 19 =
  24. 24.239 − 99 =
  25. 25.32 + 9 =
  26. 26.26 + 19 =
  27. 27.36 − 29 =
  28. 28.67 + 29 =
  29. 29.48 + 29 =
  30. 30.553 − 99 =
  31. 31.28 − 9 =
  32. 32.37 + 9 =
  33. 33.78 + 29 =
  34. 34.62 − 29 =
  35. 35.49 + 9 =
  36. 36.32 + 19 =
  37. 37.248 + 99 =
  38. 38.46 + 29 =
  39. 39.56 − 9 =
  40. 40.46 + 19 =

Answer key

  1. 620
  2. 119
  3. 53
  4. 82
  5. 70
  6. 51
  7. 637
  8. 60
  9. 61
  10. 59
  11. 82
  12. 610
  13. 76
  14. 97
  15. 98
  16. 50
  17. 55
  18. 650
  19. 52
  20. 150
  21. 39
  22. 470
  23. 77
  24. 140
  25. 41
  26. 45
  27. 7
  28. 96
  29. 77
  30. 454
  31. 19
  32. 46
  33. 107
  34. 33
  35. 58
  36. 51
  37. 347
  38. 75
  39. 47
  40. 65

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