- Christian Dorner
The process of modelling is well known. The main steps of the modelling cycle also appear in this slightly modified cycle, see gure 1 (e.g. see). In this case students rapidly start the modelling- cycle by a real world problem, here "Which credit is the best?" They translate this into a mathematical statement: "The best credit is the one with the shortest lent term." Afterwards they implement the four credits in a GeoGebra-applet. In the next stage pupils observe the dynamics and try to find coherences respectively. Following this, they should mathematically justify their observations. If the validation of the mathematical solutions brings some flaws to light, they have to start again the modelling cycle from the beginning. In this case special knowledge about credits is needed, so some stages have to be guided by the teacher.