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Let a pair of dice he rolled thrice and the random variable X be the number of doublets. Find the mean of the random variable.

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Probability of getting no doublet `=P(X=0)=5/6xx5/6xx5/6=125/216` ltbr Similary, P(X=1) `=5/6xx5/6xx1/6+1/6xx5/6xx5/6+5/6xx5/6xx1/6=75/216`
P(X=2) `=5/6xx1/6xx1/6+1/6xx5/6xx1/6+1/6xx1/6xx5/6=15/216`
P(X=3) `=1/6xx1/6xx1/6=1/216`
`therefore " " Mean =mu=125/216xx0+75/216xx1+15/216xx2+1/216xx3`
`=1/2`
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