total number of ways in which 10 examination papers be arranged = 10!
now total number of ways in which examination papers are arranged such that best and worst paper always come together =9!*2!
so number of ways in which they never come togerther = 10! -9!*2!

=8*9!

thanks but my question is when best and worst papers come together why are we taking them as 1 and subtracting 1 paper from 10 papers to get 9 and their arrangement as 9 !
i mean best paper and and worst paper cant be same as 1 .. it shud be 2 diferent papers so
whi is not 10 - 2 = 8
and arrange of 8!
final result 10!-8!x2!
<< why is it 10!-9!x2! ??????? and u shed some light ???

here's the orignal one

http://www.pagalguy.com/forum/quantitative-questions-and-answers/60879-official-quant-thread-cat-2011-a-189.html

so post here.

mods do the needful .:grin:

total number of ways in which 10 examination papers be arranged = 10!
now total number of ways in which examination papers are arranged such that best and worst paper always come together =9!*2!
so number of ways in which they never come togerther = 10! -9!*2!

=8*9!