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.)
(In reply to
13 the lucky number by Rajeev)
When I first looked at your solution I wondered how I could have missed something so simple, but on further inspection, your method requires a fourth container to hold the 2 gallons left in the 11 gallon tank so that you can put the 9 gallons in the other two tank back into the 11.
Or have I overlooked something obvious?