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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 79 · 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. 1.55 + 9 =
  2. 2.401 − 99 =
  3. 3.17 + 29 =
  4. 4.367 − 99 =
  5. 5.68 − 19 =
  6. 6.395 − 99 =
  7. 7.151 + 99 =
  8. 8.156 + 99 =
  9. 9.889 − 99 =
  10. 10.16 − 9 =
  11. 11.26 − 9 =
  12. 12.220 − 99 =
  13. 13.79 + 9 =
  14. 14.16 + 19 =
  15. 15.83 − 9 =
  16. 16.76 − 9 =
  17. 17.51 − 19 =
  18. 18.596 + 99 =
  19. 19.44 + 29 =
  20. 20.302 − 99 =
  21. 21.18 + 19 =
  22. 22.29 + 19 =
  23. 23.45 + 9 =
  24. 24.280 − 99 =
  25. 25.77 + 29 =
  26. 26.114 + 99 =
  27. 27.660 − 99 =
  28. 28.141 + 99 =
  29. 29.33 + 9 =
  30. 30.82 − 9 =
  31. 31.53 + 9 =
  32. 32.85 − 29 =
  33. 33.14 + 9 =
  34. 34.81 − 9 =
  35. 35.59 + 19 =
  36. 36.510 + 99 =
  37. 37.20 + 19 =
  38. 38.42 + 9 =
  39. 39.53 − 29 =
  40. 40.24 − 9 =

Answer key

  1. 64
  2. 302
  3. 46
  4. 268
  5. 49
  6. 296
  7. 250
  8. 255
  9. 790
  10. 7
  11. 17
  12. 121
  13. 88
  14. 35
  15. 74
  16. 67
  17. 32
  18. 695
  19. 73
  20. 203
  21. 37
  22. 48
  23. 54
  24. 181
  25. 106
  26. 213
  27. 561
  28. 240
  29. 42
  30. 73
  31. 62
  32. 56
  33. 23
  34. 72
  35. 78
  36. 609
  37. 39
  38. 51
  39. 24
  40. 15

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