ANSWER: Bring Me Exactly 7 Cups of Water
February 21st, 2006
I will give you two containers…
One holds exactly 3 cups, and the other holds exactly 5 cups.
I want you to go to the river and bring me back exactly 7 cups of water using those two containers.
The containers are not measuring containers, they have no markings. All we know is that they hold exactly 3 cups and exactly 5 cups.
You can’t estimate either. You must bring back exactly 7 cups of water.
How do you do it?
Answer:
Take the 5 cup container and fill it completely with water. Then take the 5 cup container and pour it into the 3 cup container until it is full ( you now have exactly 2 cups of water left in the 5 cup container). Now dump out the 3 cup container and pour the remaining 2 cups from the 5 cup container into the 3 cup container. Now fill up the 5 cup container completely and you have exactly 7 cups altogether!
Easy:
Fill the 5 cup with water, and then pour water from the 5 cup in the the 3 cup until the 3 cup is full.
That will leave 2 cups in the 5 cup. Discard the contents of the 3 cup and pour the 2 cups remaining in the 5 in the 3.
Then full the 5 cup again.
(5-3)+5=7