Camping with Water
RAY: Here's how you would do it. You take the seven-gallon container and you fill it up and you pour the contents of it into the 13-gallon jug. And then you do that again. And when you do that...
TOM: It's not all going to fit.
RAY: It's not all going to fit. You'll have filled the 13-gallon container, and you will have one gallon left over in the seven-gallon container.
RAY: You put that aside. You pour out the 13-gallon container. So now you have one gallon in the seven-gallon container, and the 13-gallon container is empty. You then take that one gallon and you pour it into the 13-gallon container, leaving room for 12 more gallons. You then fill the seven-gallon container again and pour the entire seven gallons into the 13 gallon container.
TOM: Now you're up to eight in there.
RAY: Now you're up to eight gallons, and you say, "Mmm. Eight. Room for how many more?"
RAY: Five. You then fill the seven-gallon container and you pour all but two gallons in, because there's only room for five in the 13-gallon container.
TOM: And you'll have two gallons left.
RAY: You'll have two gallons left, and if you don't trip and fall on the way back to the cabin, they'll be able to make the pancakes.
[ Car Talk Puzzler ]