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An exam consists of 20 multiple choice questions, each with 5 answer choices.
If a student guesses on every question, this a binomial experiment with the random variable
X
=
Number of questions answered correctly
What is the probability that the student answers exactly 4 questions correctly?
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For each question, the probability to answer correctly is = 0.8;
the probability to answer incorrectly is = 0.2.
Since this experiment is binomial, the probability under the problem's question is
P(4 of 20) = = = 1.30057E-08.
ANSWER. P(4 of 20) = 1.30057E-08.
Solved.