Over the last 100 business days, harry had 20 customers on 30 of those days, 25 customers on 20 days, 35 customers on 30 days, 40 customers on 10 days, and 45 customers on 10 days. what is the variance of the number of harry's customers?

Variance = sum of all x terms (x1 - mean of x) ^2 / n

the mean is the average: 20 + 25 + 35 + 40 + 45 / 5 = 165/5 = 33

v = (20-33) ^2 / 5 + (25-33) ^2 / 5 + (35-33) ^2 / 5 + (40-33) ^2 / 5 + (45-33) ^2 / 5

v = 33.8 + 12.8 + 0.8 + 9.8 + 28.8

v = 86