A man's car runs out of gasoline. His car tank holds exactly 13 gallons. He has three empty unmarked containers which can hold 3 gallons, 6 gallons, and 11 gallons. Using only these containers at the gas station, how can the man bring back exactly 13 gallons?

(He is not allowed to buy over 13 gallons and dispose of the extra.)

If the containers happen to have vertical sides, then a container can be half filled by tilting the container at an angle and adding just enough liquid so that the base is just covered as the liquid just starts to spill.  If you do this very carefully with the 3 and the 11, you'll have 1.5 gal in the 3, and 5.5 gal in the 11, for a total of 7 gallons.  Now just fill the 6 to the top and you have 13 gallons.

Admittedly a trick type of solution.

Posted by Larry on 2006-10-29 01:14:01