Chapter 3 - Section 3.3 - Mean, Variance, and Standard Deviation for Grouped Data - Exercises - Page 102: 3.51

mean = 150 variance = 5730.612 standard deviation = 75.7008 ∑mf represents the total average amount (in dollars) of electric bill for August of 50 families

mean = 7500\div50=150 Variance $=σ^2$ $=(∑m^2 f-([(∑mf)]^2/50-1))/50$ $= \frac{1405800- (56250000\div49)}{50}$ $=(1405800-1125000)\div50$ $=5730.612$ Standard deviation $= \sqrt 5730.612 =75.7008$