Question 464846
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Hi,
Note: The probability of x successes in n trials is: 
P = nCx* {{{p^x*q^(n-x)}}} where p and q are the probabilities of success and failure respectively. 
In this case p (guessing right) = .20 and q = .80
nCx = {{{n!/(x!(n-x)!)}}}  |20C2 = 190
P(guessing 18 out of the 20 incorrectly) = 190(.20)^2(.80)^18 =.1369