If you use only a 5-liter bowl and a 3-liter bowl and have unlimited access to water, how would you get exactly 4 liters of water in the 5-liter bowl?
Fill the 5-liter bowl and spill out 3 liters of water into the 3-liter bowl.
Then empty the 3 liter bowl so you can put the 2 liters that remains in the 5 liter bowl into the 3 -liter bowl.
Refill the 5-liter bowl and spill out 1 liter into the 3 -liter bowl (that had 2 liters in it and will now be full).
Then empty the 3 liter bowl so you can put the 2 liters that remains in the 5 liter bowl into the 3 -liter bowl.
Refill the 5-liter bowl and spill out 1 liter into the 3 -liter bowl (that had 2 liters in it and will now be full).
4 liters of water will remain in the 5-liter bowl.
