Question 854398: A student take multiple choice exam in which each question has five choices. Assuming that she has no knowledge of the correct answers to any of the questions, she has decided on a stratergy in which she will place five balls marked A,B,C,D,E into a box. She randomly selects her answer to the question. There are four multiple choice qyestion on the exam.
A. What is the probability that she will obtain full marks?
B. What is the probability tha she will get atleast three questions correct
Answer by ewatrrr(24785)   (Show Source):
You can put this solution on YOUR website!
Hi,
p(correct) = 1/5 = .2, p(incorrect) = 4/5 = .8, n = 4
P(x = 4) = (.2)^4 = .0016
B. Using TI for cumulative P: P(x ≥ 3) = 1 - binomcdf(n, p, largest x-value)
P(x ≥ 3) = 1 – P(x ≤ 2) = 1 - .9728 = .0272
or using Formula
P(x ≥ 3) = P(x=3) + P(x =4) = 4(.2)^3(.8)^1 + .0016 = .0256 + .0016 = .0272
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