Linear arrangements avoiding adjacency of two specified people: Six distinct players stand in a line. In how many ways can they be arranged if Abhinav and Manjesh are never together?

Difficulty: Medium

Correct Answer: 480

Explanation:


Introduction / Context:
To count arrangements where two specified people are not adjacent, use total permutations minus the arrangements where they are together (treated as a block) times their internal swaps.


Given Data / Assumptions:

  • Six distinct players; two are special (A, M).
  • We consider linear orderings.
  • Prohibited: A and M adjacent.


Concept / Approach:

  • Total linear orders = 6!.
  • Adjacent count: treat (A,M) as a block with 2 internal orders.
  • Not-adjacent = total − adjacent.


Step-by-Step Solution:

Total = 6! = 720Adjacent: block + 4 others → 5! arrangements, and (A,M) can be (A,M) or (M,A) → 2!, so 5!*2 = 120*2 = 240Not-adjacent = 720 − 240 = 480


Verification / Alternative check:
Gap method (place 4 others, count gaps for A and M) yields the same 480 result, confirming correctness.


Why Other Options Are Wrong:

  • 120 and 240 correspond to partial counts (e.g., adjacent cases only).
  • 360 still undercounts the exclusions.


Common Pitfalls:

  • Forgetting the 2 internal arrangements of the adjacent pair.


Final Answer:
480

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