This is a problem that I really liked and that I want to share with you. Firstly because of the story around it, secondly because of the unexpected solution, and finally because it can be investigated with a computer for those who are the least comfortable with maths.
Everybody is invited to participate, but don't forget this is for the 16 to 18 years old.
The chief of the forty thieves is finally captured and brought before the sultan, chained, and surrounded by 12 janissaries (https://en.wikipedia.org/wiki/Janissaries). The sultan tells him 'you can still save your life. Here are five black balls, and five white balls. Distribute them as you wish between these two boxes. I will then make them indistinguishable, and will shake them. You will then be blindfolded by one of my janissaries, and you will have to choose a box, and pick a ball. If the ball is white, I will spare you. If it is black ... ' and he shows him the shiny blade of his guard's scimitar (https://en.wikipedia.org/wiki/Scimitar).
How should the chief of the forty thieves make his choice in order to maximize his chances of survival ?