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.)

The only way I see of performing this without using the gauge on the pump and without having to go to your car to empty some of the gas before returning to the pump is to have a pencil, pen or some other method of marking one of the containers.  Then it is simple.

Fill the 6 gallon container.
Empty it into the 11 gallon container.
Fill the 6 gallon container again.
Use the 6 gallon container to top of the 11 gallon container.
Mark the level of gas in the six gallon container.
Pour the one gallon of gas into the 3 gallon container.
Fill the 6 gallon container back to the mark.

You now have the 13 gallons, 11 in one container and one in each of the other containers.

Edited on September 2, 2011, 8:02 pm

Posted by Joshua on 2011-09-02 20:01:57