Cars such as the Chevrolet Volt use stored battery power to propel the car for a certain number of miles and then switch to a backup gasoline powered engine once the battery is exhausted. This Demonstration computes the equivalent miles per gallon of such cars. You input how many miles the car can go on a full charge (range), what percentage of times between full charges you drive less than the range, the average number of miles you drive on days you drive more than the range, the price per gallon of gas you would pay for a similar vehicle that was purely gasoline powered, the price per gallon of gas you pay to operate the backup gasoline motor, the miles per gallon the car gets when its backup gasoline motor is used, and the price per kilowatt hour you pay to charge the car. The Demonstration outputs the probability distribution of miles between charges it will use for its computations and the equivalent miles per gallon of the car.