Reasoning

Odd Pair Out: Practice Questions with Answers

11 practice questions on Odd Pair Out, with answers; most also have an explanation or a worked solution. Try each one before you open its answer.

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1. Q.1

   Find the pair that does not belong with the others: (8,4), (12,6), (20,10), (15,6)

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   Answer: (15,6)

   Solution:

   1. Most pairs follow "second = first ÷ 2": 8÷2=4, 12÷2=6, 20÷2=10 — all match.
   2. For (15,6): 15÷2=7.5, not 6 — this pair breaks the pattern.

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2. Q.2

   Find the pair that does not belong with the others: (12,7), (15,10), (20,15), (18,11)

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   Answer: (18,11)

   Solution:

   1. Most pairs follow "first − second = 5": 12−7=5, 15−10=5, 20−15=5 — all match.
   2. For (18,11): 18−11=7, not 5 — this pair breaks the pattern.

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3. Q.3

   Find the pair that does not belong with the others: (5,30), (6,42), (7,56), (8,56)

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   Answer: (8,56)

   Solution:

   1. Most pairs follow "second = first × (first+1)": 5×6=30, 6×7=42, 7×8=56 — all match.
   2. For (8,56): 8×9=72, not 56 — this pair breaks the pattern.

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4. Q.4

   Find the pair that does not belong with the others: (2,8), (3,27), (4,64), (5,100)

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   Answer: (5,100)

   Solution:

   1. Most pairs follow "second = first³": 2³=8, 3³=27, 4³=64 — all match.
   2. For (5,100): 5³=125, not 100 — this pair breaks the pattern.

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5. Q.5

   Find the pair that does not belong with the others: (3,9), (4,16), (5,20), (6,36)

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   Answer: (5,20)

   Solution:

   1. Most pairs follow "second = first²": 3²=9, 4²=16, 6²=36 — all match.
   2. For (5,20): 5² = 25, not 20 — this pair breaks the pattern.

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6. Q.6

   Find the pair that does not belong with the others: (4,13), (6,15), (8,17), (10,18)

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   Answer: (10,18)

   Solution:

   1. Most pairs follow "second − first = 9": 13−4=9, 15−6=9, 17−8=9 — all match.
   2. For (10,18): 18−10=8, not 9 — this pair breaks the pattern.

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7. Q.7

   Find the pair that does not belong with the others: (9,3), (16,4), (25,5), (28,7)

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   Answer: (28,7) — the others pair a perfect square with its square root; 7² = 49, not 28

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8. Q.8

   Find the pair that does not belong with the others: (7,49), (8,64), (9,72), (10,100)

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   Answer: (9,72)

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9. Q.9

   Find the pair that does not belong with the others: (10,5), (16,8), (24,11), (20,10)

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   Answer: (24,11)

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10. Q.10

    Find the pair that does not belong with the others: (2,8), (3,27), (4,64), (5,126)

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    Answer: (5,126)

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11. Q.11

    Find the pair that does not belong with the others: (11,22), (14,28), (17,35), (20,40)

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    Answer: (17,35) — the others double the first number; 17 × 2 = 34, not 35

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