As a pupil I came across a problem that I called "The mean life-time of risk-takers" . Here we consider a person who is used to take a lethal risk from time to time. Assume that the risk to die is p in all cases. (Eg. p=1/6 for 'Russian Roulette', 0 < p < 1 in general). How many risk events the person survives 'in the mean' ? Of course, the mathematics of the problem has nothing to do with danger and death. It also answers how often (in the mean) one has to throw dice until one gets a six.