How do you find the number of ways to listen to 4 different CDs from a selection of 15 CDs?

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Answer 1 · 2016-02-27T02:34:06

Order doesn't matter, so we use the combination formula.

The combination formula #nC_r = (n!)/((n - r)!(r!)#

#n# is the number of elements (total).

#r# is the number of elements picked from the set.

In this case, n = 15 and r = 4

#(15!)/((11!)(4!))#

=#1365#

So, there are 1365 ways of listening to the CD's.