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?