10 books are placed at random in a shelf. The probability that a pair of books will always be together is -
Pick one.
A) 1/10  B) 9/10  C) 1/5  D) 3/10  E) 1/2
Explanation:   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   ANSWER IS 1/5
<result>C</result>
10 books are placed at random in a shelf. The probability that a pair of books will always be together is -