Answers

2014-03-31T09:20:29+05:30
1) If any arrangement is possible, there are 7! = 5040
So there are 5040 ways to arrange 7 books on a shelf.

2) If 3 particular books must always stand together, the 3 books can occupy the following positions on the shelf:

BBB----
-BBB---
--BBB--
---BBB-
----BBB


For each of these five cases, there are 3! permutations of the 3 books and 4! permutations of the other 4 books,
so the total number of allowed arrangements is 5 x 3!4! = 720.

1 5 1
2014-03-31T19:42:08+05:30
Consider 3 particular books as 1 unit 
 1 unit +remaining 4 books=5
these 5 can be placed in 120 ways   
       

0