Hi

Several students are unprepared for a multiple-choice quiz with 20 questions,

 and all of their answere are guesses. Each question has 4 possible answers,

 and only one of them is correct. P(correct) = .25 and P(incorrect)= .75

A) mean = 20*.25 = 5  SD = sqrt(20*.25*.75) = 1.9365

B) P(at least 16 correct by guessing) is so small...highly unusual.



Note: The probability of x successes in n trials is: 

P = nCx*  where p and q are the probabilities of success and failure 

respectively. In this case p = .25  and q = .75

nCx = 

 

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