Next Monday I am supposed to introduce a bunch of middle school students to Bayes' theorem.

I've scoured the Internet for basic examples where Bayes' theorem is applied. Alas, all explanations I've come cross are, I believe, difficult to grasp for the average middle school student.

So what I am looking for is a straightforward explanation of Bayes' theorem that uses the least amount of Mathematics and words possible. (Also, my presentation has to be under 3 minutes.)

I think that it would be efficient in terms of learning for me to use coins or cards, something tangible to illustrate what I'm talking about.

What do you think? How should I teach 'em Bayes' ways?

PS: I myself am new to Bayesian probability.