Question 261826
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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This is a binomial problem because the probability of guessing the right
answer on each problem is 1/4 and there are n= 20 such problems.
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a. What is the probability of getting exactly 11 correct answers?
P(x+11) = 20C11(1/4)^11(3/4)9 = binompdf(20,1/4,11) = 0.0030
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b. What is the probability of getting less than 9 correct answers?
P(0<= x <=8) = binomcdf(20,1/4,8) = 0.95907...
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I used a TI calculator to get these answers.
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Cheers,
Stan H.