Question

Debbie is borrowing 3 books from her friend who has a collection of 45 books. Which of the following expressions represents the number of ways Debbie can choose a group of 3 books?

Answer 1

you are being asked how many ways to choose 3 out of a set of 40
this is called "forty choose 3" written as
\[\dbinom{40}{3}\]
and computed by
\[\dbinom{40}{3}=\frac{40\times 39\times 39}{3\times 2}\] cancel first, multiply last

Answer 2

ok replace 40 by 45 my mistake

Answer 3

\[\dbinom{45}{3}=\frac{45\times 44\times 43}{3\times 2}\]