Here's a classic puzzle that everyone should solve at some point in their life.
Four friends are traveling at night. They have a bus to catch in 17 minutes, but it's on the other side of a questionable-looking bridge. They don't think it could reliably hold more than two people at a time. They need light to cross the bridge, but they have only one flashlight between them. Amy takes 1 minute to cross the bridge, Brian takes 2 minutes, Cassie takes 5 minutes, and Drew takes 10. If two people cross the bridge simultaneously, they must walk at the rate of the slowest person.
How can they cross in 17 minutes?
See the solution