Question 822714
Describe the probability distribution for the number of correct responses when someone makes random guesses for 10 multiple-choice questions on an SAT test. Each question has 5 possible answers (a-e), one of which is correct.
Assume that random guesses are made for each of the 10 questions. 
A. Find the mean number of correct responses.
u = np = 10*(1/5) = 2
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B. Find the standard deviation for the numbers of correct responses when random guesses are made for the 10 questions by many different subjects.
std = sqrt(npq) = sqrt(2*4/5) = 1.2649
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C. What is the probability that someone gets at least half of the questions correct?
P(10<= x <=20) = 1-P(x < 9) = 0.0026
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D. When someone makes guesses for all 10 answers, what is the expected number of correct answer?
E(x) = np = 2
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Cheers,
Stan H.
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