There are a number of "with two jugs holding x and y litres, how do I get z litres in a jug?". Well this is a slightly trickier variation on this which involves watering down milk at the same time - enjoy!
A dairyman is just about to shut for the day when two customers arrived, one carrying a half-gallon can (four pints) and the other with a quart pot (two pints). As you can see, this was in the days that customers would bring their own receptacles; however, milk can still be sold in pints.
The dairyman filled the can with four pints, and then to his dismay discovered that he had no more milk. What was he to do?
He quickly resolved to water down the milk, so that each customer had the quantity of milk that they wanted. But he wanted to make sure that both customers had milk of the same strength. He could not have one customer with weaker milk than the other, as he was a fair and just dairyman.
He looked around the dairy and the only other receptacle he could find was a three-pint jug.
So with the milk already in the half-gallon can, plenty of water in the tap, and a quart pot and three-pint jug, how does the dairyman give both customers full receptacles containing watered down milk of the same strength?
The dairyman fills the quart pot with two pints of milk from the half-gallon can, and then pours the two pints into the three-pint jug.
Then he tops up the jug with a pint of water from the tap, giving him three pints of the correct "two pints of milk to one pint of water" mixture.
This mixture is poured into the quart pot and that is ready for the owner to take home.
The remaining pint of mixture is added to the half-gallon can, and this is topped up with water from the tap.
Both vessels contain two to one mixtures and can be taken away by the customers.