Unfortunately, in Austria adolescents or young adults can't handle money in a decent[br]way. Some studies state that 14% of all visitors coming firstly in contact with the debt[br]advice service are 25 years old or younger. Actually situations become worse by taking[br]a closer look, persons of not full age hardly seek advice at an official service institution.[br]They are used to ask their friends or parents for some financial support. A smart-phone-[br]contract is the most common way for indebtedness in the youth, closely followed by a car[br]purchase. All these mentioned forms of borrowing money, even borrowing money from[br]your parents, are kinds of credits (see http://orf.at/stories/2208386/2208367/).[br]The author concentrates in his Ph.D.-thesis on financial topics, which should be taught in[br]school, focus on secondary education. He creates central ideas of financial mathematics[br]fundamental ideas in the sense of Bruner (see [2]) respectively, via an empirical study.[br]Three of these central ideas are "Use of stochastics in a nance mathematical context",[br]"time value of money" and "handling of risk". The following modelling exercise is based[br]on these mentioned ideas.[br]The Austrian school curriculum stipulates the discussion of credits in class. Furthermore[br]in Austria there are some special schools, like "Handelsakademie" (commercial high-[br]school), which deal with credits in detail. However, all considerations in school are done[br]rather statically. Changes of the interest rate are rarely discussed.[br]In addition, in a bank consultation the assistant usually shows only one credit scenario[br]which is in favour of the debtor, though this is not the only possible scenario. From the[br]point of view of banks it is obvious, they want to realize profit. So, the credit user must[br]have such knowledge in such a consultation situation.[br]At this point we explicitly emphasize: We don't want to put the reader/resp. a pupil o[br]raising a credit, but he/she should be able to understand the behaviour and the dynamics[br]of a credit and to be aware of its risks.