CONDITIONAL PROBABILTY
1. The management of a company finds that 30% of the secretaries hired are unsatisfactory. A test is created
to help screen secretarial applicants. One hundred employed secretaries are chosen at random and are given
the new test. Out of these, 90% of the satisfactory secretaries pass the test and 20% of the unsatisfactory
secretaries pass. Based on these results…
a)
if a person applies for a secretarial job, takes the test, and passes it, what is the probability that
he/she will be a satisfactory secretary?
b)
if the applicant fails the test, what is the probability that he/she will be an unsatisfactory secretary?
2. A bag contains two one‐dollar bills, a five‐dollar bill, and a ten‐dollar bill. A player draws bills one at a
time without replacement from the bag until a ten‐dollar bill is drawn. Then the game stops. All bills are kept
by the player.
a)
What is the probability of winning $16?
b)
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 Fall '07
 Epstein
 Probability, Paperback, Hardcover

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