I ran across this logic exercise in Popular Science, written by Claire Maldarelli, and thought it interesting. I tried for several days to figure it out, but ultimately, had to look at her answer to get the solution. I know you will do much better:
A Kindergartner, a fifth grader, a high school track star, and an Olympic sprinter are all waiting in line at a Track & Field meet’s food stand. Suddenly, the storm of the century rolls in and the only way back to the safety of the stadium is across a wobbly bridge in critical need of repair.
The rickety old thing can handle only two people crossing at one time.
The sky is completely black, but luckily, the Kindergartner has a flashlight key chain attached to his backpack.
The wind that will destroy the bridge arrives in 17 minutes.
The Olympic sprinter can cross the bridge in 1 minute.
The high school track star in 2 minutes.
The fifth grader in 5 minutes.
The kindergartner in 10 minutes.
One of the travelers must have a flashlight in their hand.
The minutes are counted as they traverse back and forth across the bridge (the return trip time is counted also).
Scroll down for the answer
The Olympic sprinter and the high school track star cross together first (2 minutes).
The Olympic sprinter dashes back with the light in hand (1 minute, Total =3)
Then the fifth grader and the kindergartner run across with the light (10 minutes, Total=13
The high school track star, waiting on the other side, rushes back with the flashlight to get the Olympian (2 minutes, Total=15).
Together, they run across just before the bridge collapses (2 minutes)
Total Time: 17 minutes