Count the Ways

A cage containing two dice sits next to an array of thirteen bent rods. The rods are numbered from 0 to 12. Black beads can be slid about on the rods. Visitors spin the cage then examine the dice. They can add the two dice producing a number between 2 and 12 (7, for example), then go over to bent rod number 7 and move one of the beads to record the results of this single trial. By repeatedly flipping the cage, and then moving a bead, the visitor builds up a histogram of the actual occurrence of the sum of two dice. The visitor can also choose to construct a histogram of the difference between the two dice. The resulting histograms can then be compared to the expected probabilities for the sum and difference of two dice. This exhibit is an excellent companion to the exhibit named CHASING THE ODDS, in which a computer builds the histogram a thousand times faster.
The concept of probability is one of the basic building blocks of science.