Mary is deciding whether to book the cheaper flight home from college after her exams, but she's unsure when her last exam will be. she thinks there is a 30 percent chance the exam wil be scheduled after the last day she can get the cheaper flight. If it is and she has to cancel, she will lose 100 dollars. If she takes the cheaper flight she will gain 50 dollars.
A) if she books the cheaper flight what can she expect to gain on average?
b) what is the standard deviation