Adam switches from a gas-guzzler of 12 mpg to a slightly less voracious guzzler that runs at 14 mpg. The environmentally virtuous Beth switches from a 30 mpg car to one that runs at 40 mpg. Suppose both drivers travel equal distances over a year. Who will save more gas by switching?
Beth or Adam?
Provide proof for your answer.
Now have a look at the answer, complete with explanation:
Running Down Vimy 