A student takes a multiple-choice exam. Suppose for each question he either knows the answer or gambles and chooses an option at random. Further suppose that if he knows the answer, the probability of a correct answer is 1, and if he gambles this probability is 1/4. To pass, students need to answer at least 75% of the questions correctly. The student has "studied for a minimal pass," i.e., with probability 0.75 he knows the answer to a question. Given that he answers a question correctly, what is the probability that he actually knows the answer?

A First Course in Probability (10th Edition)
10th Edition
ISBN:9780134753119
Author:Sheldon Ross
Publisher:Sheldon Ross
Chapter1: Combinatorial Analysis
Section: Chapter Questions
Problem 1.1P: a. How many different 7-place license plates are possible if the first 2 places are for letters and...
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A student takes a multiple-choice exam. Suppose for each question he either knows the
answer or gambles and chooses an option at random. Further suppose that if he knows the
answer, the probability of a correct answer is 1, and if he gambles this probability is 1/4. To
pass, students need to answer at least 75% of the questions correctly. The student has
"studied for a minimal pass," i.e., with probability 0.75 he knows the answer to a question.
Given that he answers a question correctly, what is the probability that he actually knows the
answer?
Transcribed Image Text:A student takes a multiple-choice exam. Suppose for each question he either knows the answer or gambles and chooses an option at random. Further suppose that if he knows the answer, the probability of a correct answer is 1, and if he gambles this probability is 1/4. To pass, students need to answer at least 75% of the questions correctly. The student has "studied for a minimal pass," i.e., with probability 0.75 he knows the answer to a question. Given that he answers a question correctly, what is the probability that he actually knows the answer?
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