1. Tell everyone to clear their desks. It's a pop quiz. Use your serious face.
2. Hand them this:
3. Read the questions out loud. It gets kind of fun.
4. What's the question that everyone wants to know? In my classes, it was "Wait, did I pass?" It was a smooth transition from that question to the question I asked: "Well, what are the chances that you passed?"
Then we're in familiar territory. Take guesses, write them on the board. Take ideas from the whole group. Circulate, offer suggestions, ask questions, give hints as you see fit.
The kids won't let you forget to read out the answers before the end of class.
There was a pretty interesting design question that came up as I was planning this activity: what should the quiz questions be? In order to get random guessing you just need a set of problems that kids couldn't possibly know the answers to. Here were some alternatives that I came up with when planning this problem:
In the end, I wanted a set of questions that kids could think -- just for a second -- that I actually expected them to know. So I went with some Linear Algebra pulled from a test I took in college. But something else might work for your students.