mathematics

Mary will be taking a 20-question, multiple-choice exam with three choices for each question. She has another important project to be submitted on the same day. If Mary guesses on each question of the exam, find the probability of guessing exactly 8 out of 20 correctly.

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  1. prob(correct) = 1/3
    prob(wrong) = 2/3

    prob(exactly 8 of 20 correct) = C(20,8) (1/3)^8 (2/3)^12
    = appr ......

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    Reiny

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