Re: Few questions..
I got an answer of 51,480 for the pool ball problem.
To simplify things lets say there are numbers on the 15 ball. There are 15! was to arrange the 15 balls. (You have fifteen choices for the first postion, 14 choices for the second postion, ...).
The seven red balls can be put in order in 7! ways as can the 7 yellow balls. Since we counted each ordering of the the red and yellow balls distintly, we need to divide our total by 7! twice.
15!/ (7! * 7!) = 51,480
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