OlgaN wrote:

2.What is the probability og two books being standing in adjacent places in a row of ten different books?

A 1\10

B 1\5

C 1\100

D 1\9

E 2\45

Thanks.

There are 10 books.

We can arrange total of 10 books in 10! ways.

Now, 2 books adjacent to each other can be arranged in 2 ways.

2 books together and rest of 8 books can be arranged in 9! ways.

Therefore total no of favourable ways of arrangement = 2 * 9!

Total ways of arrangement = 10!

So Required probability = 2*9!/10! = 2/10 = 1/5

Hence, B.

- Brajesh