Consider a path formed along a two mile flat stretch of road at sea level followed by a 6% grade that rises 300 feet above sea level, followed by a 1% grade that takes you back down to sea level, followed by a two mile flat stretch of road. Suppose a car at 45 mph is on cruise control and follows the path that first goes up the steep side and then down the gentler incline. At the end of the path, MPG is calculated. Then the car returns on the path at 45 mph, up the gentle incline and then down the steep incline to the end of the path. AT the end of the return trip MPG is calculated again. The speed limit on the stretch is 60 mph.
Do the trips get equal MPG, or is one direction providing better MPG than the other. If so which one and why? Would the answer change if driving at the speed limit both ways?
This question came to me while driving through hills in my 2010 Prius, but I see no reason why it should be limited to that particular car.