You have a 6-liter and 10-liter jug. Measure exactly 2 liters.
You have a 3-liter jug and a 5-liter jug, but no measuring marks. How can you measure exactly 4 liters of water?
You have a 4-liter jug and a 9-liter jug. Using only these jugs and an unlimited water source, measure exactly 6 liters.
You have a 2-liter jug and a 7-liter jug. Measure exactly 1 liter of water.