Choose the group which is different from the others :
- (a) 17, 37, 47, 97
- (b) 31, 41, 53, 67
- (c) 71, 73, 79, 83
- (d) 83, 89, 91, 97 ✓ UPSC's answer
Why the answer is (d)
• Option (d) contains 83, 89, 91, and 97; while 83, 89, and 97 are prime, 91 is a composite number (7 × 13).
• Therefore, group (d) is the only set that includes a non-prime number, making it different from the others.
Why the other options are wrong
- (a) 17, 37, 47, 97
- All numbers in this group (17, 37, 47, 97) are prime, so it does not differ from groups (b) and (c).
- (b) 31, 41, 53, 67
- All numbers in this group (31, 41, 53, 67) are prime, so it does not differ from groups (a) and (c).
- (c) 71, 73, 79, 83
- All numbers in this group (71, 73, 79, 83) are prime, so it does not differ from groups (a) and (b).
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2023, held on 28 May 2023. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.