Paper 1 · Mathematical Reasoning and Aptitude
Find the odd number pair: 23 : 29, 19 : 25, 13 : 17, 3 : 5.
A23 : 29
B19 : 25 ✓ Correct
C13 : 17
D3 : 5
Correct answer: (B) 19 : 25 — 19 : 25 is the odd pair, so that is the answer.
Explanation
★19 : 25 is the odd pair, so that is the answer.
★In each pair both numbers should be prime.
★23 and 29, 13 and 17, and 3 and 5 are all pairs of prime numbers.
★In 19 : 25, the number 19 is prime but 25 is not, since 25 is 5 times 5.
★So this pair does not have both numbers prime.
★So the odd pair is 19 : 25.
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