A student takes an exam containing 19 true or false question

A student takes an exam containing 19

true or false questions. If the student guesses, what is the probability that he will get exactly 3

questions right? Round your answer to four decimal places.

Solution

Note that the probability of x successes out of n trials is          
          
P(n, x) = nCx p^x (1 - p)^(n - x)          
          
where          
          
n = number of trials =    19      
p = the probability of a success =    0.5      
x = the number of successes =    3      
          
Thus, the probability is          
          
P (    3   ) =    0.001848221 = 0.0018 [ANSWER]