Question

Find the number of ways to listen to four CDs from a selection of 8 CDs.? A. 1680 B. 336 C. 70 D. 50

Answer 1

`""^8P_4 = 1680`, i.e. choice A.

Explanation:

Note that the order of the CDs does matter, so we are wanting `""^8P_4` rather than `""^8C_4` ...

`""^8P_4 = (8!)/((8-4)!) = 8*7*6*5 = 1680`

In other words, there are `8` choices for the first CD, `7` for the second, `6` for the third and `5` for the fourth.