JEE Advanced Mathematics question

The number of different ways in which 8 persons can stand in a row so that between two particular persons A and B there are always two persons, is

(A)Correct
(B)
(C)
(D)none of these

Answer: (A)

Solution

Choose the 2 persons who stand between A and B: ways. Treat the block "A \_ \_ B" as one unit; together with the remaining 4 persons there are 5 units, arranged in ways. Inside the block, A and B can be interchanged () and the two middle

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Question ID VK-108196