In: Statistics and Probability
5. Professor Frank Nabarro insists that all senior physics majors take his notorious physics aptitude test. The test is so tough that anyone not going on to a career in physics has no hope of passing, whereas 55% of the seniors who do go on to a career in physics still fail the test. Further, 70% of all senior physics majors in fact go on to a career in physics. Assuming that you fail the test, what is the probability that you will not go on to a career in physics? (Round your answer to four decimal places.) HINT [See Example 3.]
given :
P(fail | not going on to a career in physics) = 100% = 1
P(fail | going on to a career in physics) = 55% = 0.55
P(going on to a career in physics) = 0.70
P(not going on to a career in physics) = 1-0.70 = 0.30
P(fail) = P(fail | not going on to a career in physics)*P(not going on to a career in physics) + P(fail | going on to a career in physics)*P(going on to a career in physics)
= 1*0.30 + 0.55*0.70
P(fail) = 0.685
bayes theorem :
Assuming that you fail the test, what is the probability that you will not go on to a career in physics :
using bayes theorem :
P(not go on to a career in physics | fail) = P(fail | not going on to a career in physics)*P(not going on to a career in physics) / P(fail)
= 1*0.30 / 0.685
P(not go on to a career in physics | fail) = 0.438
Assuming that you fail the test, the probability that you will not go on to a career in physics is 0.438
P.S. (please upvote if you find the answer satisfactory)