# Random exchange rate and random interest rate

Unfortunately, one can't predict all these influences. Hence, we assume the key interest rate  as a sequence, like the exchange rate before. We start at p0 = 7 and define pn+1 = pn+X, where X is a random variable with distribution N(0; 0.42). We choose the values p0 and , such that pn hardly takes negative values. For more realistic demands one has to be careful to avoid negative values strictly. Furthermore realistic values are currently very small, therefore some visual effects don't emerge. Nevertheless, we develop further the GeoGebra applet and get the following:

## Figure 4.2

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