Use Bayes’ rule to find the indicated probability.
An water well is to be drilled in the desert where the soil is either rock, clay or sand. The
probability of rock P(R) = 0.53. The clay probability is P(C) = 0.21. The sand probability is P(S) =
0.26. It if it rock, a geological test gives a positive result with 35% accuracy. If it is clay, this test
gives a positive result with 48% accuracy. The test gives a 75% accuracy for sand. Given the test is
positive, what is the probability that soil is rock, P(rock | positive)?
P(rock | positive) = 0.405
P(rock | positive) = 0.53
P(rock | positive) = 0.209
P(rock | positive) = 0.385
Mr. Cameron is sponsoring an summer concert. He estimates that he will make $300,000 if it does
not rain and make $60,000 if it does rain. The weather bureau predicts the chance of rain is 0.34 for
the day of the concert. What are Mr. Cameron’s expected concert earning?
List the outcomes of the sample space.
A 6–sided die is rolled. The sides contain the numbers 1, 2, 3, 4, 5, 6. List the sample space of rolling
one die.
A fair coin is tossed three times, and a player wins $3 if 3 tails occur, wins $2 if 2 tails occur and
loses $3 if no tails occur. If one tail occurs, no one wins. What is the expected value of the games?