6.4. Is it possible to measure out exactly 4 liters of water into the larger of the two containers, using only a 3-liter and a 5-liter container, from a tap? If so, provide an example of how to do it.
Solution. You can, fill up 5 liters, pour 3 liters into the second container, then pour out this water, leaving 2 liters in the 5-liter container. Transfer these 2 liters to the 3-liter container. Fill the 5-liter container to the top and top up the second container (exactly 1 liter), then you will have 4 liters left in the first container. (There are other solutions as well)