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Big-Daddy
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Homework Statement
I have n elements, of which I take x and arrange them, with repetitions allowed (i.e. if one of my elements is A, and x=3, then {A,A,A} would be an acceptable permutation). Among the original n elements is the letter A, present a times, and the letter B, present b times; of these, I have selected among my x, the letter A c times, and the letter B d times. Of my x elements now, how many permutations are there? Assume the other elements are present only once each in n.
Homework Equations
nPr=n!/(n-r)!
nCr=n!((n-r)!r!)
Permutations with repetition = xx
The Attempt at a Solution
I'm thinking something like C(n-a-b,x-c-d) to account for the number of ways to choose, multiplied by (x-c-d+2)^x to account for perms. But I could be on the completely wrong track here.