In how many ways can 10 books be arranged on a shelf such that a particular pair of books should always be together?	Choose the most appropriate option:
A) 9! x 2!	B) 5!	C) 3!	D) 9!	E) 2!
We have a total of 10 books.   Given that a particular pair of books should always be together. Hence, just tie these two books together and consider as a single book.   Hence we can take total number of books as 9. These 9 books can be arranged in 9P9 =9!=9! ways.   We had tied two books together. These books can be arranged among themselves in 2P2 =2!=2! ways.   Hence, required number of ways   =9!×2!   9! x 2!ns: 9! x 2!
<result>A</result>
In how many ways can 10 books be arranged on a shelf such that a particular pair of books should always be together?