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    Question

    An unbiased coin is tossed until a head appears. The

    expected number of tosses required is
    A 1 Correct Answer Incorrect Answer
    B 2 Correct Answer Incorrect Answer
    C 4 Correct Answer Incorrect Answer
    D ∞ Correct Answer Incorrect Answer

    Solution

    Let X denote the number of tails tossed before the head appears. Then X is a geometric random variable. P(head) = 1 / 2 and the expectation is E(X)=1 / (1/2) = 2.

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