Suppose that 30% of all students who have to buy a textbook for a particular course want a new copy, whereas the other 70% want a used copy. Consider a random sample of 25 students.
(b) Suppose that new copies cost \$100 and used copies cost \$70. Assume the bookstore currently has 50 new copies and 50 used copies. What is the expected value of total revenue from the sale of the next 25 copies purchased?
I know that for expected value $E(X)=\sum_x h(x)*p(x),$ and for problems with constants, it would be a $E(x)+b.$ I just don't know how to apply that here.