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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 101 · 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. 1.80 + 29 =
  2. 2.76 − 19 =
  3. 3.38 + 29 =
  4. 4.375 − 99 =
  5. 5.44 − 29 =
  6. 6.72 − 19 =
  7. 7.513 − 99 =
  8. 8.63 − 29 =
  9. 9.76 − 9 =
  10. 10.650 − 99 =
  11. 11.58 + 9 =
  12. 12.739 + 99 =
  13. 13.65 + 29 =
  14. 14.23 − 19 =
  15. 15.66 + 19 =
  16. 16.439 − 99 =
  17. 17.91 − 29 =
  18. 18.354 + 99 =
  19. 19.31 + 19 =
  20. 20.238 − 99 =
  21. 21.63 + 9 =
  22. 22.33 + 9 =
  23. 23.20 + 29 =
  24. 24.53 + 9 =
  25. 25.18 − 9 =
  26. 26.59 + 9 =
  27. 27.31 + 29 =
  28. 28.78 + 9 =
  29. 29.22 − 9 =
  30. 30.541 + 99 =
  31. 31.219 + 99 =
  32. 32.61 − 19 =
  33. 33.371 + 99 =
  34. 34.32 + 19 =
  35. 35.71 − 9 =
  36. 36.471 + 99 =
  37. 37.190 − 99 =
  38. 38.51 − 19 =
  39. 39.42 − 19 =
  40. 40.208 + 99 =

Answer key

  1. 109
  2. 57
  3. 67
  4. 276
  5. 15
  6. 53
  7. 414
  8. 34
  9. 67
  10. 551
  11. 67
  12. 838
  13. 94
  14. 4
  15. 85
  16. 340
  17. 62
  18. 453
  19. 50
  20. 139
  21. 72
  22. 42
  23. 49
  24. 62
  25. 9
  26. 68
  27. 60
  28. 87
  29. 13
  30. 640
  31. 318
  32. 42
  33. 470
  34. 51
  35. 62
  36. 570
  37. 91
  38. 32
  39. 23
  40. 307

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