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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 251 · 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. 1.56 − 9 =
  2. 2.247 − 99 =
  3. 3.45 − 29 =
  4. 4.71 + 29 =
  5. 5.49 − 29 =
  6. 6.29 + 19 =
  7. 7.289 + 99 =
  8. 8.234 + 99 =
  9. 9.40 + 9 =
  10. 10.86 − 29 =
  11. 11.74 − 29 =
  12. 12.35 + 19 =
  13. 13.80 − 9 =
  14. 14.54 − 9 =
  15. 15.94 − 19 =
  16. 16.75 + 29 =
  17. 17.74 + 29 =
  18. 18.268 − 99 =
  19. 19.593 + 99 =
  20. 20.271 + 99 =
  21. 21.16 + 19 =
  22. 22.185 − 99 =
  23. 23.63 + 9 =
  24. 24.572 − 99 =
  25. 25.577 + 99 =
  26. 26.76 + 19 =
  27. 27.57 − 9 =
  28. 28.167 + 99 =
  29. 29.44 − 19 =
  30. 30.39 − 9 =
  31. 31.75 − 9 =
  32. 32.51 + 9 =
  33. 33.107 − 29 =
  34. 34.55 − 9 =
  35. 35.583 − 99 =
  36. 36.126 + 99 =
  37. 37.53 + 19 =
  38. 38.43 − 9 =
  39. 39.23 − 9 =
  40. 40.37 + 19 =

Answer key

  1. 47
  2. 148
  3. 16
  4. 100
  5. 20
  6. 48
  7. 388
  8. 333
  9. 49
  10. 57
  11. 45
  12. 54
  13. 71
  14. 45
  15. 75
  16. 104
  17. 103
  18. 169
  19. 692
  20. 370
  21. 35
  22. 86
  23. 72
  24. 473
  25. 676
  26. 95
  27. 48
  28. 266
  29. 25
  30. 30
  31. 66
  32. 60
  33. 78
  34. 46
  35. 484
  36. 225
  37. 72
  38. 34
  39. 14
  40. 56

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