You are a hero with a broken sword (Conan, Boromir, or your favourite Dungeons and Dragons character) being chased by a troop of bad guys (bandits, orcs, . . .). Fortunately you are on a horse and they are not. Unfortunately your horse is tired and they will eventually run you down. Fortunately you have a bow. Unfortunately you have only ten arrows. And there are 40 bad guys. Fortunately, being a hero, you never miss. The bad guys are strung out behind you, as shown. USE ECONOMICS TO GET AWAY
Note: You cannot talk to the bad guys. They are willing to take a substantial chance of being killed in order to get you--after all, they know you are a hero and are still coming. They know approximately how many arrows you have.