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Oct 3, 2014

# How many wayscan nine examination papers can pe arranged so that the best and worst papers are never together?

In how many  ways can 9 examination papers can pe arranged so that the best and worst papers are never together?

Raghunath Reddy

Member since Apr 11, 2014

Sol: Total number of arrangements that can be made in 9 papers = 9! Ways. Let the Best and Worst paper together as one unit and remaining 7 can be 7 units.These can be arranged amongst themselves as 8! Ways. In each of these arrangements the Best and Worst paper together can be arranged amongst themselves as 2! Ways. Therefore, total number of arrangements in which the Best and Worst paper together are 8!2! ways. Hence number of arrangements two particular things are never together = 9! - 8!2!.
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