There are two classes of 20 and 30 students. No student takes both classes. A student is randomly selected out of these 50 students. Let X be the number of students in the class this student is taking. Now, a class is randomly chosen (out of two). Denote by Y the number of students in this class. Which do you think is larger: E{X} or E{Y}? Explain your guess.
Find both expectations and compare.