This paper reports the results of a research about the strategies and difficulties developed by university students in the process of modeling and simulating of random phenomena in an environment of a spreadsheet. The results indicate that students had difficulties to identify key components of the problems, which are crucial to formulate a simulation model. We have identified three different schemes to generate the results of the key components, which only one of them is correct; this scheme is based in the generation of random numbers. In consequence during this investigation it was observed that the process of the instrumentation of the spreadsheet to simulate random phenomena it is complex. [For the complete proceedings, see ED584829.]