Question

Question 2: (1.5 marks) A bookshelf in a library contains 5 Math books and 15 books of other subjects. If we randomly select two books one after another and without replacement, find the probability of getting 2 math books.

Answer 1

Solution:

Given:  A bookshelf in a library contains 5 Math books and 15 books of other subjects.

thus total books are = 5 + 15 = 20

Two books are selected randomly one after another and without replacement.

We have to find:

P( getting 2 math books ) =.........?

Since two books are selected  one after another and without replacement, we use Combination formula to find number of ways.

2 math books can be selected from 5 math books in ₅C₂ ways

and any 2 books can be selected from total 20 books in ₂₀C₂ ways.

Thus

Combination formula is:

thus