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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 240 · 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. 1.457 − 99 =
  2. 2.15 + 9 =
  3. 3.255 − 99 =
  4. 4.46 − 9 =
  5. 5.40 + 9 =
  6. 6.42 + 9 =
  7. 7.83 − 19 =
  8. 8.40 + 19 =
  9. 9.575 − 99 =
  10. 10.28 − 19 =
  11. 11.74 + 9 =
  12. 12.55 + 29 =
  13. 13.22 + 9 =
  14. 14.73 + 29 =
  15. 15.54 + 19 =
  16. 16.52 + 29 =
  17. 17.48 − 9 =
  18. 18.64 + 9 =
  19. 19.36 − 19 =
  20. 20.13 − 9 =
  21. 21.40 − 29 =
  22. 22.63 + 19 =
  23. 23.623 − 99 =
  24. 24.19 + 9 =
  25. 25.34 + 19 =
  26. 26.483 − 99 =
  27. 27.35 + 29 =
  28. 28.628 + 99 =
  29. 29.14 + 9 =
  30. 30.152 + 99 =
  31. 31.69 − 29 =
  32. 32.162 − 99 =
  33. 33.436 − 99 =
  34. 34.77 − 29 =
  35. 35.21 + 29 =
  36. 36.72 − 9 =
  37. 37.62 − 29 =
  38. 38.75 + 29 =
  39. 39.542 − 99 =
  40. 40.76 − 9 =

Answer key

  1. 358
  2. 24
  3. 156
  4. 37
  5. 49
  6. 51
  7. 64
  8. 59
  9. 476
  10. 9
  11. 83
  12. 84
  13. 31
  14. 102
  15. 73
  16. 81
  17. 39
  18. 73
  19. 17
  20. 4
  21. 11
  22. 82
  23. 524
  24. 28
  25. 53
  26. 384
  27. 64
  28. 727
  29. 23
  30. 251
  31. 40
  32. 63
  33. 337
  34. 48
  35. 50
  36. 63
  37. 33
  38. 104
  39. 443
  40. 67

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