Every student from our university who has not yet taken the fundamentals of electrical engineering exam is eligable to take part.
All tools are permitted (Google, Wolfram Alpha, MATLAB, LTspice, Octave, etc.)
To avoid guessing the answer, every student had only three trials for the correct answer, that has to be within 0.1% accuracy.
We will not publish the answer, if there is no correct answer from the students.
We offered prices such as USB headsets and Bluetooth speakers.
What we were afraid about:
There will be no participation at all.
There will be a huge participation and we will not be able to quality control.
Someone (e.g. a professional from outside the university) would leak the answers.
All this did not happen...
What happened instead is:
We completed the challenge with 4 tasks.
There was one student participating that answered all 4 questions, sometimes after just half an hour, sometimes after two days.
It generated some publicity.
Even if there was only one student actively participating, We heard about lots of other students discussing the tasks, problems, usable software etc. during the semester break (in their free time).
Lots of students told us that they don't use Twitter, don't have a Twitter account, or won't setup an account just for the challenge, etc. The question is, would any other social network e.g. Facebook be more appropriate.