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A student is getting ready to take an important oral
Chapter 4, Problem 45P(choose chapter or problem)
A student is getting ready to take an important oral examination and is concerned about the possibility of having an “on” day or an “off” day. He figures that if he has an on day, then each of his examiners will pass him, independently of one another, with probability .8, whereas if he has an off day, this probability will be reduced to .4. Suppose that the student will pass the examination if a majority of the examiners pass him. If the student believes that he is twice as likely to have an off day as he is to have an on day, should he request an examination with 3 examiners or with 5 examiners?
Questions & Answers
QUESTION:
A student is getting ready to take an important oral examination and is concerned about the possibility of having an “on” day or an “off” day. He figures that if he has an on day, then each of his examiners will pass him, independently of one another, with probability .8, whereas if he has an off day, this probability will be reduced to .4. Suppose that the student will pass the examination if a majority of the examiners pass him. If the student believes that he is twice as likely to have an off day as he is to have an on day, should he request an examination with 3 examiners or with 5 examiners?
ANSWER:Step 1 of 3
\(\begin{aligned} P(X=k)= & P(X=k \mid Y=1) P(Y=1)+P(X=k \mid Y=0) P(Y=0) \\ = & \frac{1}{3}\left(\begin{array}{c} n \\ k \end{array}\right) 0.8^{k} 0.2^{n-k}+\frac{2}{3}\left(\begin{array}{c} n \\ k \end{array}\right) 0.6^{k} 0.4^{n-k} \end{aligned}\)