Question: The following distribution shows the prices of books at a college.

Class Frequency (F_i) Class Midpoint (X_i) F_iX_i

10-20 10 15 150

20-30 15 25 375

30-40 15 35 525

40-50 20 45 900

Sum = 60 = n Sum = 1950

Find:

a. The mean.

b. The variance (assume it is a population.)