Just take care not to be tempted to come up with something _you_ like/admire, but that could just pass by the intended audience... Beauty is in the mind of the viewers - so take your time to try to guess what sort of problems would impress your audience.

It very much depends on the general skills they already have, and even if they are more or less at the same level, there are so many different possible approaches. Programming problems that are like little jewels for people with a strong taste for mathematics might be entirely 'oh noooo, not again!' problems for others.

You'll see if you took the 'right' approach very soon - in the eyes of your audience.

One particular problem I remember made me love programming was the one known (if I'm right) as "Joseph's problem".

Given n entities (childs sitting in a circle, Martin, Peter, John, ...) which is the order they step out of the circle if you count them and every 'm-th' has to step out ?

It seemed so obviously simple - and still, it didn't and didn't work out correctly!! Just to be again as simple as thought in the beginning once you had the right idea about how to tackle it. Wow! :)

As a side question: do you use Perl to start teach your audience programming in general or do you start teach them Perl and they know some programming ?

Thanks.