1. The problem statement, all variables and given/known data In how many ways can you choose 30 balls from an unlimited number of blue, red, green and white balls if you can choose any number of the different coloured balls? 2. Relevant equations 3. The attempt at a solution What I did is view the problem as choosing from a set of 30 of each of blue, red, green and white balls which gives us 120, seeing that we must have ##b+r+g+w = 30##. Then the number of distinct sets is ##120 \choose 30##. Is this line of thinking correct?