Teeter
This nice applet is one of the more than 2000 GeoGebra open educational resources created by the Hungarian Geomatech project.
In this activity you are about to find out the exact weight of a man, by learning how a teeter mathematically works. When you find a solution for the set of weights being put on the right, the Hungarian question asks you to type the weight exactly.
The Geomatech project was a joint work of the Budapest Metropolitan University of Applied Sciences (formerly: BKF University) and the GeoGebra Team between 2013 and 2015, with a number of Hungarian experts in education and sciences involved.