Mr. P needs to fill his grandkids' wading pool with exactly 16 gallons of water.
He has at his disposal a 7-gallon pail, a 5-gallon pail, and water from the faucet.
How can he fill the pool exactly without wasting any water and without removing any water from the pool (water is a precious commodity in Colorado!)?

Solution to the Problem:

Here's one way to do it:

Fill the 7-gallon pail, then use it to fill the 5-gallon pail.
Dump the 2 gallons left in the 7-gallon pail into the pool.
Pour the water from the 5-gallon pail back into the 7-gallon pail.
Go to the faucet and add more water to top off the 7-gallon pail.
Dump those 7 gallons into the pool.
Fill the 7-gallon pail from the faucet and dump them into the pool.

Correctly solved by:

1. Brooks Garris Lake View High School,
Lake View, South Carolina
2. James Alarie Flint, Michigan
3. Michael Reilly Silver Spring, Maryland
4. Atul Rai New Delhi, India