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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 622 · 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. 1.76 + 9 =
  2. 2.67 + 19 =
  3. 3.411 − 99 =
  4. 4.21 + 29 =
  5. 5.46 + 9 =
  6. 6.123 + 99 =
  7. 7.75 − 9 =
  8. 8.75 − 29 =
  9. 9.627 + 99 =
  10. 10.30 + 19 =
  11. 11.98 − 19 =
  12. 12.71 − 29 =
  13. 13.71 − 9 =
  14. 14.476 + 99 =
  15. 15.68 − 19 =
  16. 16.37 + 29 =
  17. 17.60 + 29 =
  18. 18.286 + 99 =
  19. 19.448 + 99 =
  20. 20.790 − 99 =
  21. 21.79 − 19 =
  22. 22.12 − 9 =
  23. 23.87 − 9 =
  24. 24.70 + 9 =
  25. 25.57 − 9 =
  26. 26.80 − 29 =
  27. 27.38 − 29 =
  28. 28.63 − 9 =
  29. 29.36 + 19 =
  30. 30.22 − 19 =
  31. 31.515 + 99 =
  32. 32.79 + 9 =
  33. 33.85 − 29 =
  34. 34.47 − 9 =
  35. 35.699 − 99 =
  36. 36.98 − 29 =
  37. 37.358 − 99 =
  38. 38.93 − 29 =
  39. 39.25 − 9 =
  40. 40.754 + 99 =

Answer key

  1. 85
  2. 86
  3. 312
  4. 50
  5. 55
  6. 222
  7. 66
  8. 46
  9. 726
  10. 49
  11. 79
  12. 42
  13. 62
  14. 575
  15. 49
  16. 66
  17. 89
  18. 385
  19. 547
  20. 691
  21. 60
  22. 3
  23. 78
  24. 79
  25. 48
  26. 51
  27. 9
  28. 54
  29. 55
  30. 3
  31. 614
  32. 88
  33. 56
  34. 38
  35. 600
  36. 69
  37. 259
  38. 64
  39. 16
  40. 853

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