Suppose that consumption of electricity per day depends on two prices, daily price of $0.06 per kilowatt hour (KWH) and $0.1/KWH in the evening. It was detected that consumers of electricity purchased 2,000 KWH of electric during the day and 1,600 KWH in the evening. Using middle point formula, the price elasticity of the demand for electricity is equal to: 0.5 -0.5