Students didn’t perform any real design tasks prior to this activity, but they were familiar with this type of qualitative problem-solving approach from similar questions encountered during the theoretical study. This task requires a sound conceptual understanding of the principles underlying the subject of simple electric circuits. In the course of its solution, students confront some of the most common difficulties and misconceptions in the domain. If they cannot discover the solution from theoretical consideration only, the simulation can be of great help. Even if the theoretical design is correct, there is a second difficulty in implementing the design in reality.