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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 667 · 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. 1.862 − 99 =
  2. 2.358 − 99 =
  3. 3.614 + 99 =
  4. 4.108 − 29 =
  5. 5.17 + 19 =
  6. 6.54 − 29 =
  7. 7.816 − 99 =
  8. 8.888 − 99 =
  9. 9.69 + 9 =
  10. 10.37 + 19 =
  11. 11.56 + 9 =
  12. 12.24 + 9 =
  13. 13.451 + 99 =
  14. 14.79 + 9 =
  15. 15.59 − 9 =
  16. 16.464 − 99 =
  17. 17.74 − 29 =
  18. 18.86 − 9 =
  19. 19.32 − 19 =
  20. 20.20 − 9 =
  21. 21.67 + 19 =
  22. 22.77 − 9 =
  23. 23.65 + 9 =
  24. 24.74 + 9 =
  25. 25.35 − 29 =
  26. 26.469 + 99 =
  27. 27.704 − 99 =
  28. 28.613 + 99 =
  29. 29.138 + 99 =
  30. 30.76 + 9 =
  31. 31.60 − 19 =
  32. 32.22 + 9 =
  33. 33.41 + 9 =
  34. 34.44 + 19 =
  35. 35.59 + 19 =
  36. 36.14 + 29 =
  37. 37.84 − 9 =
  38. 38.53 − 29 =
  39. 39.656 − 99 =
  40. 40.53 − 9 =

Answer key

  1. 763
  2. 259
  3. 713
  4. 79
  5. 36
  6. 25
  7. 717
  8. 789
  9. 78
  10. 56
  11. 65
  12. 33
  13. 550
  14. 88
  15. 50
  16. 365
  17. 45
  18. 77
  19. 13
  20. 11
  21. 86
  22. 68
  23. 74
  24. 83
  25. 6
  26. 568
  27. 605
  28. 712
  29. 237
  30. 85
  31. 41
  32. 31
  33. 50
  34. 63
  35. 78
  36. 43
  37. 75
  38. 24
  39. 557
  40. 44

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