Mary is deciding whether to book the cheaper flight home from college after her final​ exams, but​ she's unsure when her last exam will be

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Mary is deciding whether to book the cheaper flight home from college after her final​ exams, but​ she's unsure when her last exam will be. She thinks there is only a 10​% chance that the exam will be scheduled after the last day she can get a seat on the cheaper flight. If it is and she has to cancel the​ flight, she will lose ​\$300.
If she can take the cheaper​ flight, she will save ​\$150
.
​a) If she books the cheaper​ flight, what can she expect to​ gain, on​ average?
​b) What is the standard​ deviation?

Apply the variance formula below.

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If she books the cheaper​ flight, what can she expect to​ gain, on​ average?

The expected value of a discrete random variable is found by multiplying each possible value by the probability that it​ occurs, and then finding the sum. Use the formula​ below, where x represents a possible value of the random variable and​ P(x) is the probability that it occurs.

Expected savings  = -0.1*300 + 150*0.9  = \$105

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