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mr_coffee

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**How many permutation of abcde are there in which ... confused!**

Hello everyone I'm lost on this problem, it says:

How many permutations of abcde are there in which the first character is a, b, or c and the last character is c, d, or e?

They say:

The number of elements in a certain set can be found by computing hte number in some larger universe that are not in the set and subtracting this from the total.

I'm not sure what "larger universe" I'm suppose to find..

I nkow the inclusion/exculsion rule can be used to compute the number that are not in the set but the examples in the book don't seem to help me.

If I let A = {a, b, c} and B = {c, d, e}

then A U B = {a, b, c, d, e}

A Insersect B = {c}

N(A U B) = N(A) + N(B) - N(A intersect B); <-- that's the incuslion/exclusion rule...

ANy help would be great

thanks!