vineetbatra wrote:Mike, a DJ at a high school radio station, neeeds to play two or three more songs before the end of the school dance. if each composition must be selected from a list of 10 most popular songs of the year, how many song sequences are available for the remainder of the dance.
1. 6
2. 90
3. 165
4. 720
5. 810
Is this a combination problem or a permutation problem, and why?
If the question asks how many 'sequences' are possible, then order is certainly important; it's a permutations question, not a combinations question. That said, the wording of the question is pretty bad. Parts of it aren't even grammatical, and it isn't at all clear whether Mike is allowed to play the same song twice. From the answer choices, it's clear he's not; if he plays two songs, he has 10 choices for the first and 9 for the second, so 10*9 = 90 sequences in total. If he plays three songs he has 10, 9 and 8 choices, so 10*9*8 = 720 sequences in total, giving us a total of 90 + 720 = 810 sequences.
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