Actually, this question first involves COMBINATIONS and then PERMUTATIONS.
We first must calculate how many combinations can 5 things can be chosen from 7. The formula is: n! / r! *(n -r)! = 7! / 5! * 2! = 7 * 6 * 5! / 5 ! * 2 = 7 * 6 / 2 = 21 ways we can choose 5 things from 7 objects.
Now we must see how many permutations there are of 5 things: 5 * 4 * 3 * 2 * 1 = 120
That means we can put each of the 5 song combinations into 120 "5 song sequences". So, the total number of ways is 21 * 120 = 2,520 possible ways.
