The Monty Hall Problem
2/5
In a contest there are three doors. Behind one there is a car and behind the other two there are goats. You choose a door. The presenter, who knows where the...
Chance and uncertainty
Riddles that sharpen probabilistic intuition and decision-making under uncertainty.
The envious dice
3/5
There are four special dice: - A: 4, 4, 4, 4, 0, 0 B: 3, 3, 3, 3, 3, 3 C: 6, 6, 2, 2, 2, 2 D: 5, 5, 5, 1, 1, 1 You choose a die first. The dealer then choose...
The last passenger
3/5
An airplane has \(n\) seats and \(n\) passengers, each with their assigned seat. Passenger 1 loses his card and sits randomly in any seat. Starting with pass...
White balls in two boxes
3/5
You have 50 white balls and 50 black balls. You must divide them into two boxes, with the only condition that neither is left empty. Then one of the two boxe...
The envelope and the banknotes
3/5
There are two envelopes. One contains twice as much money as the other. You choose one at random and open it: inside there is €20. They offer you to change t...
The shared birthday
3/5
There are several people in a room. We will assume that birthdays are distributed evenly over the 365 days of the year and that there are no leap years. How...
The choice optimal
3/5
You interview candidates for a job, one by one and in random order. You can only choose one, and once you reject a candidate you can't go back. You want to m...
The coin justa
3/5
You have a skewed coin, but you don't know how much. It can come up heads more times than tails, or the other way around; all you know is that its bias is fi...
The prisoner and the two urns
2/5
A prisoner receives 50 white balls and 50 black balls. You must distribute them between two urns, however you want, but no urn can be left empty. Then the ja...
The cita of the quince minutes
4/5
Two friends meet to meet between 6:00 and 7:00. Each one arrives at random at some point during that hour. Whoever arrives first will wait exactly 15 minutes...
The broken stick
3/5
You break a stick at two points chosen at random, and thus obtain three pieces. What is the probability that these three pieces can form a triangle?
Three chinchetas in a plato
2/5
Three thumbtacks are placed randomly on the edge of a circular plate. What is the probability that there is some semicircle that contains all three?
The urn that reveals itself
4/5
An urn contains 100 balls. Some are red and the rest are green. You don't know how many red ones there are, except this: the number of red balls was chosen a...