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GATE 2021 IN – Question 5

General Aptitude · Analytical Aptitude: Logical Reasoning and Deduction · 1 mark · Multiple choice

Four persons P, Q, R, S sit in a row facing the same direction. P and R cannot sit adjacent; S must sit to the right of Q. The number of distinct arrangements is ______.

  1. 2
  2. 4
  3. 6
  4. 8

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Show answer and explanation

Correct answer: (C) 6

Explanation

There are 4!=24 unrestricted arrangements. Treat adjacent P,R as one block: 2·3!=12 arrangements are forbidden. Of the remaining 12, swapping Q and S pairs one arrangement with S right of Q and one with S left. Exactly **6, C** qualify.