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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 721 · 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. 1.21 + 29 =
  2. 2.84 − 19 =
  3. 3.72 + 29 =
  4. 4.156 + 99 =
  5. 5.56 + 9 =
  6. 6.78 − 19 =
  7. 7.40 + 9 =
  8. 8.19 − 9 =
  9. 9.840 − 99 =
  10. 10.66 + 9 =
  11. 11.723 + 99 =
  12. 12.659 + 99 =
  13. 13.47 − 9 =
  14. 14.34 − 9 =
  15. 15.73 + 19 =
  16. 16.97 − 19 =
  17. 17.27 + 29 =
  18. 18.20 + 9 =
  19. 19.15 + 9 =
  20. 20.92 − 29 =
  21. 21.58 + 19 =
  22. 22.37 + 19 =
  23. 23.419 − 99 =
  24. 24.48 − 9 =
  25. 25.51 + 19 =
  26. 26.81 − 19 =
  27. 27.240 + 99 =
  28. 28.25 + 29 =
  29. 29.787 + 99 =
  30. 30.16 − 9 =
  31. 31.69 + 29 =
  32. 32.60 + 29 =
  33. 33.76 + 9 =
  34. 34.461 + 99 =
  35. 35.87 − 9 =
  36. 36.55 + 19 =
  37. 37.151 − 99 =
  38. 38.38 + 29 =
  39. 39.30 + 9 =
  40. 40.65 − 19 =

Answer key

  1. 50
  2. 65
  3. 101
  4. 255
  5. 65
  6. 59
  7. 49
  8. 10
  9. 741
  10. 75
  11. 822
  12. 758
  13. 38
  14. 25
  15. 92
  16. 78
  17. 56
  18. 29
  19. 24
  20. 63
  21. 77
  22. 56
  23. 320
  24. 39
  25. 70
  26. 62
  27. 339
  28. 54
  29. 886
  30. 7
  31. 98
  32. 89
  33. 85
  34. 560
  35. 78
  36. 74
  37. 52
  38. 67
  39. 39
  40. 46

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