One end of a string of length L is attached to a nail driven into a wall. A small ball is attached to the other end of the string. Another nail is driven into the wall a distance l directly underneath the first nail.

A student holds the ball so that the string is horizontal and parallel to the wall. The student then releases the ball. Subsequently, the string wraps around the “bottom” nail. What is the minimum distance l that allows for that to happen?

The readers sent us quite a few solutions to our September Challenge, Second to one, submitted by Philip Blanco. It was great to see many first-time solvers. It is our hope that the teachers will continue to encourage their students to send us their solutions. As always, we would also love to see more reader-contributed Challenges.

We are pleased to recognize the...

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