Run the Count Buffon needle experiment. It consists of participants throwing a needle or a wooden stick onto a sheet of paper or card which has a series of parallel lines drawn onto it. The probability of the needle or stick intersecting a line is a fraction involving pi. By counting the fraction of intersections, as more and more needles/sticks are thrown, an approximation to pi should be obtained. We did this at my former college years ago,. Perversely, the more results we got, the further we moved from pi !