A die is thrown three times. Let `X` be the number of twos seen. Find the expectation of `X` .

Explanation

We have, X= number of two seen


So, on throwing a die three times, we will have X=0,1,2,3


P(X=0)=P(not2)​⋅P(not2)​⋅P(not2)​=`5/6​xx5/6​xx5/6​=125/216`
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P(X=1)=P(not2)​⋅P(not2)​⋅P(2)​+P(not2)​⋅P(2)​⋅P(not2)​+P(2)​⋅P(not2)​⋅P(not2)​


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