Brainteaser #5 – Dividing Marbles


You do not remember where you were, nor do you know where you are. Once you open your eyes to the darkness of a soft cloth hood draped over your head, though, you have a sneaking suspicion…

You then hear footsteps getting closer as someone walks slowly to towards you in what sounds like an empty warehouse. Now you fear the worst. 

The hood is removed and your interrogator is looking at you dead in the eye. You fear the worst. 

However, you are spared an unlikely challenge, a chance to pardon yourself and live another day!

You are showed 100 marbles, 50 of which are red and 50 of which are blue. You have two empty containers in front of you.

The interrogator gives you the instructions: 

“Divide these 100 marbles into the two containers. You can divide them however you want, but you will have to use all the marbles. The hood will then go back on your head and the containers mixed up. 

You will remove ONE marble from ONE container. If it is BLUE you survive. If it is RED, you will die.”

How do you divide the marbles between the containers to give you the best chance of survival?

You place one blue marble in one bowl, and then place every single other marble in the other bowl (49 blues and 50 reds). Now, when you go to pick a marble, you will have a 50/50 chance of picking the bowl with the one blue marble, and thus, you will survive. If, however, you pick the other bowl then you have almost a 50/50 chance of picking a blue marble.

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