Question

A computer user has downloaded 15 songs using an online file-sharing program and wants to create a CD-R with 13 songs to use in his portable CD player. If the order that the songs are placed on the CD-R is not important to him, how many different CD-Rs could he make from the 15 songs available to him?

Answer 1

If the order of the songs on the CD-R is not important, the computer user can create different CD-Rs by selecting any combination of 13 songs out of the 15 available. The number of different CD-Rs that can be made is given by the combination formula:

C(15, 13) = 15! / (13! * (15-13)!) = 105 different CD-Rs.