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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 849 · 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. 2.42 + 9 =
  3. 3.47 − 29 =
  4. 4.77 − 9 =
  5. 5.363 + 99 =
  6. 6.64 − 19 =
  7. 7.31 + 19 =
  8. 8.39 + 9 =
  9. 9.396 + 99 =
  10. 10.62 − 19 =
  11. 11.74 + 9 =
  12. 12.182 − 99 =
  13. 13.286 − 99 =
  14. 14.158 + 99 =
  15. 15.80 + 9 =
  16. 16.113 + 99 =
  17. 17.49 − 29 =
  18. 18.47 − 9 =
  19. 19.61 − 29 =
  20. 20.49 + 19 =
  21. 21.616 + 99 =
  22. 22.88 − 19 =
  23. 23.814 − 99 =
  24. 24.289 + 99 =
  25. 25.34 + 9 =
  26. 26.22 − 19 =
  27. 27.541 − 99 =
  28. 28.73 + 9 =
  29. 29.76 + 19 =
  30. 30.24 + 9 =
  31. 31.160 − 99 =
  32. 32.48 − 19 =
  33. 33.45 − 29 =
  34. 34.61 − 9 =
  35. 35.359 − 99 =
  36. 36.15 − 9 =
  37. 37.21 − 9 =
  38. 38.41 + 9 =
  39. 39.23 − 9 =
  40. 40.327 + 99 =

Answer key

  1. 21
  2. 51
  3. 18
  4. 68
  5. 462
  6. 45
  7. 50
  8. 48
  9. 495
  10. 43
  11. 83
  12. 83
  13. 187
  14. 257
  15. 89
  16. 212
  17. 20
  18. 38
  19. 32
  20. 68
  21. 715
  22. 69
  23. 715
  24. 388
  25. 43
  26. 3
  27. 442
  28. 82
  29. 95
  30. 33
  31. 61
  32. 29
  33. 16
  34. 52
  35. 260
  36. 6
  37. 12
  38. 50
  39. 14
  40. 426

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