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 getexactly7 correct is?

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- Nov 16th 2008, 12:55 PMArythDiscrete Probability Distributions
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? - Nov 16th 2008, 01:07 PMPlato
$\displaystyle {15 \choose 7}(s)^7(1-s)^{15-7}$

Where $\displaystyle s$ is the probability of success. - Nov 16th 2008, 01:12 PMAryth
Thanks, and I assume that s would be 0.25 because of four possible choices and one correct answer.