Find the odd one out in the set: {19, 37, 21, 17, 25, 29, 31} A. 21 B. 37 C. 29 D. 23

GATE 2024 · General Aptitude · Odd One Out · easy

Answer: A. 21

1. Check each number for primality: 19 — prime. 37 — prime. 17 — prime. 29 — prime. 31 — prime. 21 = 3 x 7 — composite. 25 = 5 x 5 — composite. Wait: 25 is also composite. But 25 is not listed in the options; only 21, 37, 29, 23 are options. The set {19,37,21,17,25,29,31} contains 21 and 25 as composites, but only 21 appears as an answer option.
2. Identify the answer option that is not prime: Among the four answer choices — 21, 37, 29, 23 — only 21 = 3 x 7 is composite. The question asks for the odd one out from the set, and 21 is the composite number among the answer options, making it the number that does not share the prime property.