SOLUTION: A quiz consists of 20 multiple-choice questions, each with 5 possible answers. For someone who makes random guesses for all of the answers, find the probability of passing if the m

 

Hi

A quiz consists of 20 multiple-choice questions, each with 5 possible answers

 P(passing) if the minimum passing grade is 70 %. |that is, 14 or more correct

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 = 1/5 = .2 and q = .8

nCx = 

For example:

 P(x = 14) =  30C14(.2)^14(.8)^6 = 38,760(.2)^14(.8)^6 = .0000016647

 P(x ≥ 14) = P(14)+P(15)+P(16)+P(17)+P(18)+P(19)+P(20) = .000001845