SOLUTION: I need help in this question. I know that n=15 and p=0.2 and q=0.8. But don't quite understand what the question meant by omits one of the wrong answers and guesses the other 3. Pl

Algebra ->  Probability-and-statistics -> SOLUTION: I need help in this question. I know that n=15 and p=0.2 and q=0.8. But don't quite understand what the question meant by omits one of the wrong answers and guesses the other 3. Pl      Log On


   

Question 269482: I need help in this question. I know that n=15 and p=0.2 and q=0.8. But don't quite understand what the question meant by omits one of the wrong answers and guesses the other 3. Please help.
A Multiple-choice test has 15 questions with each having 5 possible answers with one correct. Assume a student answers every question, omits one of the wrong answers on each question and randomly guesses among the remaining three choices.
Answer by drk(1908) About Me  (Show Source):
You can put this solution on YOUR website!
You start with 5 possible answer choices. So if you randomly guess,
P(correct) = .20, and P(incorrect) = .80
To omit one question means remove one answer choice that is obviously wrong. You are left with 4 answer choices, not 3 as stated in the question. So, if you randomly now guess
P(correct) = .25, and P(incorrect) = .75
Now the expression for P( n correct) is
p%28n+correct%29+=+%2815cn%29%2A%281%2F4%29%5E%28n%29%2A%283%2F4%29%5E%2815-n%29