You have a 3-liter jug and a 5-liter jug, and you need to measure out exactly 4 liters of water. You can use the jugs to pour water back and forth, but you do not have any markings on the jugs to measure the volume of the water. You also do not have any other containers or instruments that you can use. How can you measure out exactly 4 liters of water using only the two jugs?
(For the answer scroll down to the bottom of the page).
Answer: Fill the 3-liter jug with water and pour it into the 5-liter jug. Then fill the 3-liter jug with water again and pour it into the 5-liter jug until it is full. This will leave 1 liter of water in the 3-liter jug. Empty the 5-liter jug, and then pour the 1 liter of water from the 3-liter jug into the 5-liter jug. Finally, fill the 3-liter jug with water again and pour it into the 5-liter jug until it is full, bringing the total volume of the water in the 5-liter jug to exactly 4 liters.
