[Math] How many ways are there to distribute 2 indistinguishable white and 4 indistinguishable black balls into 4 indistinguishable boxes

combinatoricsprobabilityprobability distributionsprobability theory

How many ways are there to distribute 2 indistinguishable white and 4 indistinguishable black balls into 4 indistinguishable boxes?

How can we solve this?

Best Answer

There are 5 essentially different ways to distribute the black balls. In each case I'll count the essentially different ways of distributing the white balls.

4, 0, 0, 0

The possible distinguishable ways of distributing the white balls are: 2-0-0-0, 1-1-0-0, 0-2-0-0 and 0-1-1-0. So 4 is the number.

3, 1, 0, 0

Here we can do it like this: 2-0-0-0, 1-1-0-0, 1-0-1-0, 0-2-0-0, 0-1-1-0, 0-0-2-0, 0-0-1-1. So 7.

2, 2, 0, 0

Once again: 2-0-0-0, 1-1-0-0, 1-0-1-0, 0-0-2-0, 0-0-1-1. 5 ways.

2, 1, 1, 0

And again: 2-0-0-0, 1-1-0-0, 1-0-0-1, 0-2-0-0, 0-1-1-0, 0-1-0-1, 0-0-0-2. 7 ways.

1, 1, 1, 1

Lastly: 2-0-0-0, 1-1-0-0. 2 ways.

In total, $4+7+5+7+2 = 25$ ways to distribute the balls.