Question

Mrs. Reid is going on a trip. She has 9 books that she hasn't read yet, but she wants to bring only 3 on the trip. In how many ways can she choose 3 books to bring on the trip?

♦27
♦84
♦504
♦60,480

Answer 1

Option B is right.

Explanation:

Given that there are totally 9 books unread by Mrs. Reid. OUt of these she wants to take only 3 books on the trip.

For books order does not count.

Hence combinations would be appropriate to calculate.

3 books out of 9 can be selected in

9C 3 ways

No of ways of selecting 3 books for the trip out of 9 =
`(9(8)(7))/(1(2)(3)) =84`

There are just 84 ways of choosing 3 books to bring on the trip out of 9 unread books.

Option B is right.