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ONU Problem of the Week

Solving a math problem is like crossing a bridge. It takes one step at a time. (photo/

Solving a math problem is like crossing a bridge. It takes one step at a time. (photo/

It’s a dark night, and Crosby, Stills, Nash, and Young come to a narrow bridge over a crocodile infested river, which they must all cross. At most, two of them can cross the bridge at one time. They have only one flashlight, which is needed to cross the bridge safely. Each of the four are able to walk across the bridge at a different maximum possible individual speed, and any pair walking across the bridge together must walk at the speed of the slower one. Crosby can cross the bridge in 20 minutes, Stills in 10 minutes, Nash in four minutes, and Young in two minutes.

What is the minimum length of time it can take for all four to cross the bridge?


Congratulations to the 35 Ohio Northern University students who obtained all five points for the previous ONU Problem of the Week. Senior mechanical engineering major Dylan Dolph won the random drawing to receive the $10 gift certificate to Cosi. 

Solutions for this problem must be submitted to Dr. Robinson by Thursday, April 6. Solutions can be slipped under Dr. Robinson’s office door (Mathile 214), handed to the Department of Mathematics & Statistics administrative assistant, sent via e-mail (, or sent by campus mail. Please include on all submissions your name, major, email address, campus address, and phone number. You must show your work.

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