So if you have 12 CDs and you are choosing 4 for one evening you get 8 more CDs for 3 evening.So what i did is 12 - 4 and it is equal to 8 CDs and You divide 4 in to 12 and it gives you 3.Your answer is 3 order of CDs because the question is asking how many order of CDs are possible for playing 4 CDs?
