In April of 2015, this puzzle was posed to me by Daryl, a long-time Kiva RV Park and Horse Motel resident who is sharper than a tack and has had a lifetime of experiences.

Here we go!

Your milkman stops by to deliver milk. All he has are 10 gallon jugs filled with milk. You only want to purchase 4 gallons… but you only have an empty 3 gallon and 5 gallon jug. All the jugs only have FULL indicators. Note that the milkman wants to keep all of his 10 gallon jugs.

How do you exactly measure out 4 gallons of milk, just using the 3 available jugs?

There are two solutions.

Solution 1:

Fill up the 3 gallon jug from the 10 gallon one, and then dump those 3 gallons into the 5 gallon jug.

Fill up the 3 gallon jug again from the milkman’s 10 gallon jug, then use the 3 gallon jug to fill up the 5 gallon jug which removes 2 gallons from your 3 gallon jug and leaves 1 gallon.

Dump the entire contents of the 5 gallon jug back into the milkman’s jug.

Put the 1 gallon that was left over in the 3 gallon jug into the 5 gallon jug.

Fill the 3 gallon jug from the milkman’s jug.

Voila! You now have 3 gallons in one jug and 1 gallon in the other for a total of 4 gallons.

Recap

Solution 2:

Fill up the 5 gallon jug from the 10 gallon one, and then pour 3 of those gallons into the 3 gallon jug, leaving 2 gallons in the 5 gallon jug.

Empty the 3 gallon jug back into the milkman’s jug.

Put the 2 gallons that are in the 5 gallon jug into the 3 gallon jug.

Fill the 5 gallon jug from the milkman’s jug.

Fill up the 3 gallon jug from the 5 gallon jug by pouring 1 gallon, leaving 4 gallons left in the 5 gallon jug.

Voila, now your 5 gallon jug is holding 4 gallons of milk.

To wrap up, pour all the milk from the 3 gallon jug back into the milkman’s jug.

Recap