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Odd One Out Worksheet for Maths Olympiad

Maths Olympiad topic 7: Odd one out · Set 52 · 40 questions
TalentJR

How to solve it (Find the shared rule): Check whether all the numbers are odd or all even — if so, look deeper. Try the tables 3, 4, 5, 6, 7, 8 and 9: which one has three of the numbers in it? The number that is not in that table is the odd one out.

NameDateTime takenScore ___ / 40
  1. 1.Which is the odd one out: 27, 81, 63, 49? (a) 27 (b) 81 (c) 63 (d) 49
  2. 2.Which is the odd one out: 16, 20, 40, 14? (a) 16 (b) 20 (c) 40 (d) 14
  3. 3.Which is the odd one out: 42, 48, 12, 24? (a) 42 (b) 48 (c) 12 (d) 24
  4. 4.Which is the odd one out: 45, 65, 81, 27? (a) 45 (b) 65 (c) 81 (d) 27
  5. 5.Which is the odd one out: 45, 63, 81, 35? (a) 45 (b) 63 (c) 81 (d) 35
  6. 6.Which is the odd one out: 18, 20, 48, 40? (a) 18 (b) 20 (c) 48 (d) 40
  7. 7.Which is the odd one out: 50, 18, 48, 72? (a) 50 (b) 18 (c) 48 (d) 72
  8. 8.Which is the odd one out: 55, 35, 77, 49? (a) 55 (b) 35 (c) 77 (d) 49
  9. 9.Which is the odd one out: 12, 72, 36, 16? (a) 12 (b) 72 (c) 36 (d) 16
  10. 10.Which is the odd one out: 32, 16, 70, 80? (a) 32 (b) 16 (c) 70 (d) 80
  11. 11.Which is the odd one out: 42, 40, 20, 48? (a) 42 (b) 40 (c) 20 (d) 48
  12. 12.Which is the odd one out: 45, 27, 81, 85? (a) 45 (b) 27 (c) 81 (d) 85
  13. 13.Which is the odd one out: 10, 12, 40, 48? (a) 10 (b) 12 (c) 40 (d) 48
  14. 14.Which is the odd one out: 63, 49, 27, 81? (a) 63 (b) 49 (c) 27 (d) 81
  15. 15.Which is the odd one out: 24, 50, 30, 48? (a) 24 (b) 50 (c) 30 (d) 48
  16. 16.Which is the odd one out: 62, 16, 32, 64? (a) 62 (b) 16 (c) 32 (d) 64
  17. 17.Which is the odd one out: 38, 32, 48, 12? (a) 38 (b) 32 (c) 48 (d) 12
  18. 18.Which is the odd one out: 24, 30, 16, 20? (a) 24 (b) 30 (c) 16 (d) 20
  19. 19.Which is the odd one out: 24, 20, 40, 18? (a) 24 (b) 20 (c) 40 (d) 18
  20. 20.Which is the odd one out: 24, 22, 16, 48? (a) 24 (b) 22 (c) 16 (d) 48
  21. 21.Which is the odd one out: 16, 24, 32, 30? (a) 16 (b) 24 (c) 32 (d) 30
  22. 22.Which is the odd one out: 80, 16, 28, 40? (a) 80 (b) 16 (c) 28 (d) 40
  23. 23.Which is the odd one out: 30, 64, 32, 24? (a) 30 (b) 64 (c) 32 (d) 24
  24. 24.Which is the odd one out: 45, 27, 85, 81? (a) 45 (b) 27 (c) 85 (d) 81
  25. 25.Which is the odd one out: 74, 64, 48, 24? (a) 74 (b) 64 (c) 48 (d) 24
  26. 26.Which is the odd one out: 24, 48, 14, 12? (a) 24 (b) 48 (c) 14 (d) 12
  27. 27.Which is the odd one out: 40, 18, 24, 20? (a) 40 (b) 18 (c) 24 (d) 20
  28. 28.Which is the odd one out: 16, 22, 20, 40? (a) 16 (b) 22 (c) 20 (d) 40
  29. 29.Which is the odd one out: 26, 30, 12, 60? (a) 26 (b) 30 (c) 12 (d) 60
  30. 30.Which is the odd one out: 20, 48, 32, 24? (a) 20 (b) 48 (c) 32 (d) 24
  31. 31.Which is the odd one out: 54, 18, 12, 52? (a) 54 (b) 18 (c) 12 (d) 52
  32. 32.Which is the odd one out: 27, 45, 81, 65? (a) 27 (b) 45 (c) 81 (d) 65
  33. 33.Which is the odd one out: 96, 32, 36, 64? (a) 96 (b) 32 (c) 36 (d) 64
  34. 34.Which is the odd one out: 40, 48, 18, 20? (a) 40 (b) 48 (c) 18 (d) 20
  35. 35.Which is the odd one out: 27, 35, 63, 81? (a) 27 (b) 35 (c) 63 (d) 81
  36. 36.Which is the odd one out: 16, 32, 64, 82? (a) 16 (b) 32 (c) 64 (d) 82
  37. 37.Which is the odd one out: 48, 32, 96, 62? (a) 48 (b) 32 (c) 96 (d) 62
  38. 38.Which is the odd one out: 32, 28, 56, 64? (a) 32 (b) 28 (c) 56 (d) 64
  39. 39.Which is the odd one out: 70, 80, 32, 64? (a) 70 (b) 80 (c) 32 (d) 64
  40. 40.Which is the odd one out: 35, 45, 81, 27? (a) 35 (b) 45 (c) 81 (d) 27

Answer key

  1. 49
  2. 14
  3. 42
  4. 65
  5. 35
  6. 18
  7. 50
  8. 55
  9. 16
  10. 70
  11. 42
  12. 85
  13. 10
  14. 49
  15. 50
  16. 62
  17. 38
  18. 30
  19. 18
  20. 22
  21. 30
  22. 28
  23. 30
  24. 85
  25. 74
  26. 14
  27. 18
  28. 22
  29. 26
  30. 20
  31. 52
  32. 65
  33. 36
  34. 18
  35. 35
  36. 82
  37. 62
  38. 28
  39. 70
  40. 35

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