WBCS Preliminary Examination 2024 — General Studies · Question 28 of 200

Answer: (B) 36

24, 72 and 168 are all multiples of 24 ($24 \times 1$, $24 \times 3$, $24 \times 7$), but 36 is not ($36 \div 24 = 1.5$), so 36 is the odd one out. A second test gives the same answer: 36 is the only perfect square ($6^2$) in the list. In odd-number-out questions, check in this order: divisibility by a common factor, squares and cubes, prime or composite, and sum of digits, then pick the option that fails a property shared by the other three.