Question 560851
Her test is 20 multiple choice questions with 5 possible answers each. She has no choice but to guess on each question.
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Binomial Problem with n = 20 and p(correct) = 1/5
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a. How many questions can Elizabeth expect to get correct by guessing?
Ans: np = 20*(1/5) = 4
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b. What is the probability that she passes the test? (Her final grade is at least a 70.)
P(14 <= x <= 20)) = 1 - binomcdf(20,0.2,13) = 0.000001845
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c. What is the probability that Elizabeth answers only 5 questions correctly?
P(x = 5) = 20C5(1/5)^5*(4/5)^15 = 0.1746
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d. What is the probability that she answers less than 10 questions incorrectly?
P(0<= x <= 9) = binomcdf(20,0.2,9) = 0.9861
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Cheers,
Stan H.
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