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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 675 · 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. 1.572 + 99 =
  2. 2.38 − 9 =
  3. 3.39 − 9 =
  4. 4.175 + 99 =
  5. 5.13 − 9 =
  6. 6.477 + 99 =
  7. 7.98 − 29 =
  8. 8.726 + 99 =
  9. 9.51 + 9 =
  10. 10.103 − 29 =
  11. 11.533 + 99 =
  12. 12.51 − 29 =
  13. 13.571 − 99 =
  14. 14.598 + 99 =
  15. 15.23 + 19 =
  16. 16.16 + 9 =
  17. 17.65 − 19 =
  18. 18.19 + 9 =
  19. 19.63 + 29 =
  20. 20.64 + 19 =
  21. 21.451 + 99 =
  22. 22.68 − 19 =
  23. 23.58 − 29 =
  24. 24.13 + 19 =
  25. 25.80 + 29 =
  26. 26.61 + 9 =
  27. 27.18 + 29 =
  28. 28.621 − 99 =
  29. 29.66 + 9 =
  30. 30.43 + 29 =
  31. 31.270 − 99 =
  32. 32.69 + 29 =
  33. 33.41 + 19 =
  34. 34.24 − 9 =
  35. 35.76 − 9 =
  36. 36.29 + 19 =
  37. 37.58 + 9 =
  38. 38.45 + 19 =
  39. 39.149 + 99 =
  40. 40.64 − 29 =

Answer key

  1. 671
  2. 29
  3. 30
  4. 274
  5. 4
  6. 576
  7. 69
  8. 825
  9. 60
  10. 74
  11. 632
  12. 22
  13. 472
  14. 697
  15. 42
  16. 25
  17. 46
  18. 28
  19. 92
  20. 83
  21. 550
  22. 49
  23. 29
  24. 32
  25. 109
  26. 70
  27. 47
  28. 522
  29. 75
  30. 72
  31. 171
  32. 98
  33. 60
  34. 15
  35. 67
  36. 48
  37. 67
  38. 64
  39. 248
  40. 35

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