Question

In how many ways can 7 different books be arranged in a shelf? In how many ways can we arrange three particulars books so that they are always together?

Answer 1

We need to find the number of ways in which 7 different books can be arranged in a shelf.

We also need to arrange three particular books so that they are always together.

For this, we assume the three books as one book for the time being.

Now, we have 5 books. These books can be arranged in

The three books can be arranged in 3 × 2 = 6 ways among themselves.

Thus, the required number of ways is 120 × 6 = 720.