Question 264581: A multiple choice test has 20 questions with each having 4 possible answers with one correct. Assume a student randomly guesses the answer to every question
a. What is the probability of getting exactly 9 correct answers?
b. What is the probability of getting less than 9 correct answers?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! A multiple choice test has 20 questions with each having 4 possible answers with one correct. Assume a student randomly guesses the answer to every question
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Binomial Problem with n = 20, p = 1/4
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a. What is the probability of getting exactly 9 correct answers?
P(x=9) = 20C9(1/4)^9(3/4)^11) = 0.02706...
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b. What is the probability of getting less than 9 correct answers?
P(0<= x <=8) = binomcdf(20,4^-1,8) = 0.9591...
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Cheers,
Stan H.
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