Kobal, Damjan2013-12-182013-12-182008http://hdl.handle.net/2003/3155810.17877/DE290R-13228We present two simple but very applicable mathematical ideas. The idea of an arithmetic mean, is used in car differential (differential gear). The idea of continuous and discrete functions is applied in modern electronic communications. Both ideas are very useful to present and motivate the interdisciplinary approach and intuitive value of abstract mathematical ideas in teaching.enGesellschaft für Didaktik der Mathematik510conference contribution