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husnain

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From: Chichawatni,Pakistan

Registered: 2014-10-03

Posts: 8,129

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Combination:

Question:
In how many ways can 10 examination papers be arranged so that the best and the worst papers never come together?

Option A):
9*8!
Option B):
8*8!
Option C):
8*9!
Option D):
7*9!

Correct Answer is Option C):
8*9!

Explanation:
No. of ways in which 10 paper can arranged is 10! Ways.
When the best and the worst papers come together, regarding the two as one paper, we have only 9 papers.
These 9 papers can be arranged in 9! Ways.
And two papers can be arranged themselves in 2! Ways.
No. of arrangement when best and worst paper do not come together,
= 10!- 9!.2! = 9!(10-2) = 8.9!.

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