This exhibit is about how to save time by rolling over. You see a picture in front of you with lots of colored Smarties. Your task is to count them, or at least determine the approximate number. But mathematicians are usually lazy when it comes to rather “boring” tasks. So how can the task be accomplished in a relatively short time with a suitable tool? At hand is a small plastic frame that encloses a relatively small number of Smarties, one holds it over the picture.

If you now count the Smarties in the frame and calculate how many frames you would need to cover the picture, you get a rollover for the total number of Smarties as a product of both numbers.

This method of simplifying the solution to a problem by proceeding systematically is of central importance in mathematics. This exhibit can be understood by elementary school children — but the basic idea behind it is universal. See also the exhibit: “3 times 4”.

Figure 1: The “Smarties” exhibit