How many ways can you choose 2 books from a shelf of 40 books

Hence, the number of ways of doing so is:

                                780 ways.

Step-by-step explanation:

We know that if we have to choose r items out of a total of 'n' items then the number of ways of doing so is calculated by the formula of combination as:

which is given by:

Here we have to chose 2 books out of a shelf of 40 books.

i.e. we have: n=40 and r=2

Hence, the number of ways of doing so is:

            Hence, the answer is:

                   780

25% is the answer