SOLUTION: How to do this problem Willard has just been given a ten question multiple choice test in one of his classes. each question has five answers only one of which is correct. Since wi
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Question 450293: How to do this problem Willard has just been given a ten question multiple choice test in one of his classes. each question has five answers only one of which is correct. Since willard has not attended class recently, he does not know any of the answers. assume that willard guesses randomly on all ten questions. Find the probability that he will answer at most 3 questions correctly.
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
The probability of 
successes in 
trials where 
is the probability of success on any given trial is given by:
\ =\ \left(n\cr k\right\)\left(p\right)^k\left(1\,-\,p\right)^{n\,-\,k})
Where )
is the number of combinations of things taken at a time and is calculated by !})
+
You need the probability that he will score 0, 1, 2, OR 3, so:
\ =\ \sum_{i\,=\,0}^3\ \left(10\cr\ i\right\)\left(0.2\right)^i\left(0.8\right)^{10\,-\,i})
John
My calculator said it, I believe it, that settles it
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