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


Given that, X= no. of twos seen


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



P(X=1) = Pnot 2. Pnot 2. P2 + P 2. P2. Pnot 2 + P 2. Pnot 2. P 2





P(X=2) =Pnot 2. P2. P2 + Pnot 2. P2. P2 + P2. Pnot 2.P2








We know that,





28
1