A multiple-choice examination has 15 questions. Each question has four possible answers of which only one is correct. The probability that by just guessing a student will get exactly 7 correct is?
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$\displaystyle {15 \choose 7}(s)^7(1-s)^{15-7}$ Where $\displaystyle s$ is the probability of success.
Thanks, and I assume that s would be 0.25 because of four possible choices and one correct answer.
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