The bridge and the lantern
2/5
Four people must cross a bridge at night. They only have one flashlight, and no one can cross without it. A maximum of two people can cross at a time. Each p...
Timeless ingenuity
Timeless classics of mathematical ingenuity and logical elegance.
The hourglasses
1/5
You have two hourglasses: one measures 7 minutes and the other measures 11 minutes. You have no other instrument to measure time. How can you measure exactly...
The two ropes
2/5
You have two ropes and a lighter. Each rope takes exactly one hour to burn completely, but it does not burn evenly: one half can take much longer than the ot...
The wolf, the goat and the cabbage
2/5
A farmer must cross a river with a wolf, a goat and a cabbage. The boat can only carry the farmer and one of the other three. If you leave the wolf alone wit...
The tower of Hanoi
3/5
There are three rods and a tower of 7 discs of different sizes, stacked from largest to smallest on one of them. You can only move one disk at a time and you...
The three vessels of the wise man (India antigua)
2/5
A wise man has three vessels of 12, 8 and 5 liters. The 12 is full; the other two, empty. You must divide the contents into two equal parts, using only trans...
The inheritance of the 17 camels (Arab tradition)
2/5
A father leaves 17 camels to his three children with these conditions: - the oldest corresponds to \(1/2\) ; to the second, \(1/3\) ; to the minor, \(1/9\) ....
The Chinese Farmer's Riddle
2/5
A farmer buys 100 animals for exactly 100 coins. - Each buffalo costs 10 coins. Each pig costs 3 coins. Each chicken costs 1/2 coin. How many animals of each...
The wise men and the perlas (Persia antigua)
2/5
A sultan has 9 seemingly identical pearls, but one weighs a little more than the others. You have a two-pan scale and want to identify the heaviest pearl usi...
The Lo Shu magic square (China)
2/5
Place the numbers 1 through 9 in a 3\times 3 grid, using each number only once, so that the sum of each row, each column, and each diagonal is 15. Give a val...
A cyclic elimination
3/5
The positions of a circle are numbered from 1 to \(n\) . Position 2 is eliminated first, then 4, then 6, and so on, continuing in a circular manner between t...
The elephant and the boat
2/5
A rajah wants to find out how much his elephant weighs, but he doesn't have a scale capable of supporting it. It does have the following: a boat that perfect...
Six vasos
1/5
Six identical glasses are lined up on a table. The first three are full of water and the last three are empty: full, full, full, empty, empty, empty You can...
The four tortugas
2/5
Four turtles occupy the four corners of a square 10 centimeters on a side. They all start moving at the same time and at the same speed. Each one always adva...
The palo of the hundred hormigas
2/5
A straight stick measures 1 meter. On it there are 100 ants, in any positions. They all move at 1 centimeter per second. Each one initially chooses one of th...
The monk and the mountain
1/5
A monk climbs a mountain along a narrow path. It leaves at dawn and reaches the summit at dusk. Spend the night there. The next day go down the same path. It...