10 books are placed at random in a shelf. The probability that a pair of books will always be together is
Options:
(A) 1/10
(B) 9/10
(C) 1/5
(D) 3/10
(E) 1/2 Hmmm, my stream of consciousness:
user
10 books can be rearranged in 10! ways consider the two books taken as a pair then number of favourable ways of getting these two books together is 9! 2!
Required probability = 1/5 So, the answer is (C).
assistant