UPSC Prelims 2023 CSAT Paper II · Q40 of 77 Mental Ability easy

Choose the group which is different from the others :

  1. (a) 17, 37, 47, 97
  2. (b) 31, 41, 53, 67
  3. (c) 71, 73, 79, 83
  4. (d) 83, 89, 91, 97 ✓ UPSC's answer

Why the answer is (d)

• Option (a) contains 17, 37, 47, and 97, all of which are prime numbers.

• Option (b) contains 31, 41, 53, and 67, all of which are prime numbers.

• Option (c) contains 71, 73, 79, and 83, all of which are prime numbers.

• 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.

Reading the answer is not the same as getting it right under a clock. Practise this question with UPSC's negative marking, and anything you miss goes into an error notebook until you get it right twice.

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