document.write( "Question 1102406: A quiz consists of 20 multiple-choice questions, each with 4 possible answers. For someone who makes random guesses for all of the answers, find the probability of passing if the minimum passing grade is 60 %. \n" ); document.write( "

Algebra.Com's Answer #717161 by rothauserc(4718) $\"\"$ $\"About$

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To get 60%, the person needs to get 12 answers correct(0.60 * 20)
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\n" ); document.write( "probability(p) of guessing correctly on a problem is 1/4 = 0.25
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\n" ); document.write( "we use the binomial probability formula
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\n" ); document.write( "Probability (k successes out of n trials) = nCk * p^k * (1-p)^(n-k), where p is probability of a success, nCk = n! / (k! * (n-k)!)
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\n" ); document.write( "for this problem n=20, k=12, p = 0.25
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\n" ); document.write( "P (12 successes out of 20 trials) = 20C12 * (0.25)^12 * (1-0.25)^(20-12) = 0.00075
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\n" ); document.write( "Probability of getting 60% on the quiz by guessing is 0.00075
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\n" ); document.write( "good reason to study :-)
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