Remark. Another way to obtain the preceding formula for the joint probabilitymass function is to regard all the n balls as distinguishable from each other. Then,since the outcome of the experiment is an ordering of these balls, it follows thatthere are n! equally likely outcomes. Finally, because the number of outcomes having special and nonspecial balls in specified places is equal to the number of ways ofpermuting the special and the nonspecial balls among themselves, namely k!(n − k)!,we obtain the preceding density function.
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