Me and my wife are often not knowing which DVD to watch. If we have two options we have a simple solution, I put one DVD in one hand behind my back and the other DVD in the other hand. She will randomly choose a hand and the DVD I have in that hand will be the one to watch.
This procedure is easy to expand to any power of 2. If we have 4 DVD's I hold 2 in one hand, 2 in the other. When a pair of DVD's is chosen, I split them out to two hands and she choses again.
The question is, what can we do when we have 3 DVD's. The assumptions we make are:
- I am not impartial. If I can influence the result somehow I will try to do that
- My wife really choses randomly a side every-time, independent of what she chose earlier.
- I don't have any other place to hide the DVD's, so every DVD is either visible or in one of the two hands.
As requirement we have that it must be a procedure with a predetermined number of steps. Not more, not less. If this is not possible, a solution that guarantees to finish with an upperbound, this is a good second choice. Off course the DVD we choose must be really random!