Expert: Laramy Wells - 8/16/2006

Question
This movie has riddles.  There is one riddle that I don't understand.  The one where they are in the park and have a 5 gallon jug and a 3 gallon jug.  They have to measure exactly 4 gallons of water.  I don't understand their explanation.  Can you help?

Answer
Okay, hopefully I can explain this in a way you will understand.  They fill the 3 gallon jug and then pour that into the 5 gallon jug.  Now there is 3 gallons in the 5 gallon jug.  They then fill the 3 gallon jug again.  They pour what they can into the 5 gallon jug, which is only 2 gallons since the 5 gallon jug already has 3 gallons in it.  This leaves 1 gallon in the 3 gallon jug.  Dump out the 5 gallon jug.  Pour the 1 gallon from the 3 gallon jug into the 5 gallon jug.  Now fill the 3 gallon jug one more time.  Pour that 3 gallons into the 5 gallon jug, which already has 1 gallon, and you end up with 4 gallons.

Again hope you understood that...if not let me know and I'll try it again.  I love that riddle.  I'm a high school math teacher and have used it in class before.  Thanks for the question.