New RBI Grade B 2025 Notification will come Soon! Enroll Here

    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.

    Practice Next