Dividing n balls into n buckets so 2 are empty.

197 Views Asked by At

We know that the balls and buckets are distinguishable, and n>2. I was searching the site for some clues but didn't really find any of them helpful. Any thoughts?

1

There are 1 best solutions below

9
On BEST ANSWER

I'm going to assume the question is, how many ways are there to distribute $n$ distnguishable balls among $n$ distinguishable buckets in such a way as to leave exactly two buckets empty.

First, choose the two buckets to be empty --- $n\choose2$ ways to do this.

Now you could have $3$ balls in one bucket, one ball in every other bucket. $n-2$ ways to choose the 3-ball bucket, $n\choose3$ ways to choose the balls to go in it, $(n-3)!$ ways to distribute the other balls.

Or, you could have $2$ balls in each of two buckets, one ball in each other bucket. $n-2\choose2$ ways to choose the two buckets, $n\choose4$ ways to choose the four balls that will go into those two buckets, $4\choose2$ ways to distribute the four balls to the two buckets, $(n-4)!$ ways to dispose of the other balls.

Can you combine all these numbers to get the answer?