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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 37 · 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. 1.401 + 99 =
  2. 2.388 + 99 =
  3. 3.812 − 99 =
  4. 4.68 − 29 =
  5. 5.528 + 99 =
  6. 6.31 + 9 =
  7. 7.337 − 99 =
  8. 8.56 − 29 =
  9. 9.13 + 9 =
  10. 10.183 − 99 =
  11. 11.76 − 29 =
  12. 12.224 − 99 =
  13. 13.61 + 9 =
  14. 14.304 − 99 =
  15. 15.21 − 9 =
  16. 16.815 − 99 =
  17. 17.59 − 9 =
  18. 18.568 − 99 =
  19. 19.15 + 29 =
  20. 20.50 + 9 =
  21. 21.69 + 19 =
  22. 22.40 − 19 =
  23. 23.38 + 19 =
  24. 24.40 + 9 =
  25. 25.211 + 99 =
  26. 26.53 + 9 =
  27. 27.67 − 19 =
  28. 28.57 + 19 =
  29. 29.73 + 19 =
  30. 30.102 − 29 =
  31. 31.77 + 29 =
  32. 32.15 + 19 =
  33. 33.671 + 99 =
  34. 34.89 − 9 =
  35. 35.54 + 9 =
  36. 36.35 + 29 =
  37. 37.72 − 9 =
  38. 38.67 + 29 =
  39. 39.49 − 9 =
  40. 40.207 + 99 =

Answer key

  1. 500
  2. 487
  3. 713
  4. 39
  5. 627
  6. 40
  7. 238
  8. 27
  9. 22
  10. 84
  11. 47
  12. 125
  13. 70
  14. 205
  15. 12
  16. 716
  17. 50
  18. 469
  19. 44
  20. 59
  21. 88
  22. 21
  23. 57
  24. 49
  25. 310
  26. 62
  27. 48
  28. 76
  29. 92
  30. 73
  31. 106
  32. 34
  33. 770
  34. 80
  35. 63
  36. 64
  37. 63
  38. 96
  39. 40
  40. 306

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