Unfortunately, one can't predict all these influences. Hence, we assume the key interest[br]rate [math]\left(p_n\right)_{n\ge1}[/math] as a sequence, like the exchange rate before. We start at p[sub]0[/sub] = 7 and define p[sub]n+1[/sub] = p[sub]n[/sub]+X, where X is a random variable with distribution N(0; 0.42). We choose the[br]values p[sub]0[/sub] and , such that p[sub]n[/sub] hardly takes negative values. For more realistic demands[br]one has to be careful to avoid negative values strictly. Furthermore realistic values are[br]currently very small, therefore some visual effects don't emerge. Nevertheless, we develop[br]further the GeoGebra applet and get the following:

Now there are many possible scenarios, two possibilities are shown in figure 4.[br]Again pupils shall make some observations with focus on e.g. "What is the difference[br]between the debt level pathways of credit 1, 2, 3 and the debt level pathway of credit[br]4?" or "What happens to the debt level pathway if the key interest rate increases?" or[br]"In which sense is it wise to raise credit 3?"