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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 253 · 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. 1.40 − 19 =
  2. 2.39 + 29 =
  3. 3.25 + 19 =
  4. 4.518 + 99 =
  5. 5.67 + 9 =
  6. 6.428 − 99 =
  7. 7.12 + 29 =
  8. 8.53 + 9 =
  9. 9.19 + 19 =
  10. 10.154 + 99 =
  11. 11.379 + 99 =
  12. 12.84 − 19 =
  13. 13.70 − 29 =
  14. 14.57 + 19 =
  15. 15.366 + 99 =
  16. 16.71 + 9 =
  17. 17.312 + 99 =
  18. 18.97 − 19 =
  19. 19.66 + 19 =
  20. 20.24 + 19 =
  21. 21.27 + 29 =
  22. 22.70 − 9 =
  23. 23.70 + 19 =
  24. 24.51 − 29 =
  25. 25.80 + 19 =
  26. 26.88 − 9 =
  27. 27.25 − 19 =
  28. 28.42 + 29 =
  29. 29.72 + 29 =
  30. 30.34 + 19 =
  31. 31.58 + 9 =
  32. 32.50 − 9 =
  33. 33.27 − 9 =
  34. 34.60 + 29 =
  35. 35.74 + 19 =
  36. 36.13 − 9 =
  37. 37.71 − 9 =
  38. 38.76 − 29 =
  39. 39.156 + 99 =
  40. 40.42 − 29 =

Answer key

  1. 21
  2. 68
  3. 44
  4. 617
  5. 76
  6. 329
  7. 41
  8. 62
  9. 38
  10. 253
  11. 478
  12. 65
  13. 41
  14. 76
  15. 465
  16. 80
  17. 411
  18. 78
  19. 85
  20. 43
  21. 56
  22. 61
  23. 89
  24. 22
  25. 99
  26. 79
  27. 6
  28. 71
  29. 101
  30. 53
  31. 67
  32. 41
  33. 18
  34. 89
  35. 93
  36. 4
  37. 62
  38. 47
  39. 255
  40. 13

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