Cheryl's birthday
3/5
Albert and Bernardo have just met Cheryl. She tells them that her birthday is one of these ten dates: - May 15, May 16, May 19 June 17, June 18 July 14, July...
Pure logic
A collection focused on formal deduction: clear premises, crisp inference, and minimal ambiguity.
The guardianes of the two doors
2/5
You are faced with two doors: one leads to the exit and the other to perdition. Next to them are two guardians. One always tells the truth and the other alwa...
The three mislabeled boxes
1/5
You have three closed boxes with these labels: “Apples”, “Oranges” and “Mixed”. You know all three labels are wrong. You can take a single fruit out of a sin...
The jugs of agua
1/5
You have two unmarked jugs: one with 3 liters and one with 5 liters. You have a tap with unlimited water. How can you measure exactly 4 liters?
The two broken clocks
1/5
You have two watches: - clock A is completely stopped; Clock B works, but it goes back exactly 1 minute every hour. Which of the two keeps the correct time m...
The ages in a temporal mirror
1/5
Someone says: "Now I am 40 years old, and today I am 4 times the age you were when I was the age you are now." How old are you now?
The tercer wise man ciego
3/5
Three perfectly logical wise men are sitting in a circle. The king informs them that he has five hats: three white and two black. Next, place a hat on each w...
The most difficult logic puzzle in the world
5/5
Three gods, A, B and C, are called Truth, Falsehood and Random, in some order. - Truth always answers with the truth. Falsehood always responds with a lie. R...
The three prisoners and the red hats
3/5
Three prisoners perfectly logical are in row. Each one can ver the hats of the that has delante, but no the suyo nor the of quienes are behind. The guard les...
The nine-dot puzzle
2/5
Draw these 9 points forming a \(3\times 3\) grid: Can you join the 9 dots with only 4 consecutive straight lines, without lifting the pencil from the paper?
Missionaries and cannibals
2/5
Three missionaries and three cannibals must cross a river in a boat that only accepts one or two people. On no shore can there remain a group in which the ca...
The caballero, the escudero and the spy
2/5
On an island there are three types of inhabitants: - gentlemen, who always tell the truth; squires, who always lie; spies, who can tell truth or lie. You mee...
The elimination tournament
2/5
1024 players participate in a tennis tournament in a direct elimination format. Each match eliminates exactly one player. How many games must be played to de...
The island of the ojos azules
4/5
On an island live perfectly logical people. Exactly 100 of them have blue eyes. The others have brown eyes, but no one knows the color of their own eyes. Eve...
The mentira of the monday
2/5
One person says: —Yesterday I lied. You know that this person always lies on Mondays, Tuesdays and Wednesdays, and always tells the truth on other days. What...
The coin of two heads
1/5
There are two coins in a bag: - a coin has heads on both sides; the other is a normal coin, with heads and tails. You draw one at random, toss it, and it com...
Ten tokens and the black impossible
1/5
You start with 10 white chips on the table. In each move you must choose exactly two pieces and turn them over: white goes to black and black goes to white....
The traffic light that it reprograma only
1/5
An experimental traffic light has three lights: red \(R\) , yellow \(A\) and green \(V\) . Each light is worth 1 if it is on and 0 if it is off. Each minute...
Chameleons with a possible ending
4/5
On an island there are 4 red, 7 green and 10 blue chameleons. Every time two chameleons of different colors meet, they both change to the third color. 1. Is...
Dashboard infection
4/5
On a \(100\times100\) board, exactly 99 squares start out infected. Every minute, a healthy square becomes infected if it shares a side with at least two inf...
The urn bet
4/5
An urn starts with 1 red and 1 blue ball. In each turn: a ball is drawn at random; is returned to the urn; A new ball of the same color is added. After \(n\)...
The executioner and the hats (3 colores)
4/5
There are 10 people in a row, numbered 1 to 10, where 10 is behind everyone. Each hat can be red, blue or green. Person 10 speaks first and sees the hats of...
The scale and the bola distinta
2/5
You have a balance with two pans and three visually identical balls. You know that one of them weighs differently than the other two, but you don't know if i...
The cadena of mentiras (7 in circle)
2/5
There are 7 people sitting in a circle. Each one says exactly: > “My neighbor on the right is a liar.” It is known that each person belongs to one of these t...
The squeeze party
2/5
At a party there are \(n\) people, with \(n\ge2\) . Each person writes down how many handshakes they gave during the party. Is it possible that the \(n\) num...
Six personas and a triangle social
2/5
In any meeting of 6 people, does at least one of these two things always happen? - there are 3 people who know each other; there are 3 people who are mutual...
The row impossible of cards
2/5
You start with the row of cards 4, 2, 6, 1, 5, 3. The only operation allowed is to exchange two adjacent cards whose sum is odd. Can this be achieved 1, 2, 3...
The last ball
2/5
In an urn there are black and white balls. You repeatedly draw two balls: if they are the same color, you remove them and insert a black one; If they are a d...
The four prisoners and the wall
3/5
Four prisoners, A, B, C and D, are lined up. There is a wall between C and D. - A goes to B and C. B sees C. C and D don't see anyone on the other side of th...
The marriage handshake
2/5
At a party there are several married couples. No one shakes hands with themselves or their own spouse. You ask everyone else how many hands they have shaken...
The snail in the well
1/5
A snail climbs 3 meters each day and, while sleeping at night, slides 2 meters. If the well is 10 meters deep, in how many days will it come out?
The mixed pills
1/5
A person must take one blue and one red pill each day. He has exactly two blue and two red left. By accident they get mixed up and you can no longer distingu...
The four cards
2/5
There are four cards on the table. Each one has a letter on one side and a number on the other. You see these faces: A D 4 7 You want to check if this rule i...
The fair counting of the loaves
2/5
Two travelers cross the desert. One carries 5 loaves. The other has 3 loaves. Halfway there they are joined by a third traveler, who does not bring food. The...
The nativos in circle
3/5
An anthropologist is surrounded by a circle of natives. Each one belongs to one of two tribes: those who always tell the truth; those who always lie. He asks...
The three logical in the bar
2/5
A waiter approaches a table where there are three logicians and asks them: “Do you three want beer?” The first one answers: “I don't know.” The second answer...
The hundred logical numerados
3/5
In a room there is a hundred logicians. The first one says: “There is exactly 1 liar here.” The second says: “There are exactly 2 liars here.” The third says...
The two islanders
2/5
A judge visits an island where everyone belongs to one of two tribes: the truthful, who always tell the truth; the liars, who always lie. He meets two island...