In how many ways can 10 examination papers be arranged so that the best and the worst papers never come together?
Correct Answer : B.
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!.