Each of five boxes contains 3 blue,1 red and 2 black pens. Independently draw one pen uniformly from each box. If X₁ counts blue pens and X₂ counts red pens,find P(X₁=2,X₂=1).
The required color counts are (2,1,2),with probabilities (1/2,1/6,1/3). The multinomial probability is 5!/(2!1!2!)·(1/2)²·(1/6)·(1/3)²=30/216=**5/36, A**.
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