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From $3$ red, $4$ green and $5$ yellow balls, how many selections consisting of $6$ balls are possible, if each color must be represented twice?

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    Could you provide some background why you are interested in this question. If it is a homework, please include the homework task. Also indicate if you did already try something? Maybe with a smaller number of balls?2012-11-13
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    It is an exercise in an old textbook (Statistics: A Foundation for Analysis by Hughes and Grawoig). According to the answers there should be 180 selections consisting of 6 balls with each color having two representations. Because there are several like objects, the total number of permutations should be 27,720.2012-11-13

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