**Hopefully this one is not actually a chestnut **
A military tank needs to cross a two hundred mile dessert (a straight flat path). The tank can travel 1 mile per gallon of gas and can only hold 40 gallons of gas in its tank. The tank is carrying its maximum capacity when it contains 40 gallons of gas (so you may not store additional gas anywhere on the tank); however, your crew knows of a way to store gas in the desert sand for retrieval at a later time. Presume that you have an infinite source of gas at the starting point. How much gas will it take to cross the dessert? How many times would you need to turn back towards the starting source? How many miles will you travel?
Edited by BMAD, 20 February 2013 - 10:32 PM.