The three mislabeled boxes
Level 1 · Starter · ●○○○○
You have three closed boxes with labels: "Apples", "Oranges" and "Mixed". You know all three labels are wrong. You can take only one fruit from a single box...
Timeless ingenuity
Timeless classics of mathematical ingenuity and logical elegance.
The round sewers
Level 2 · Core · ●●○○○
Why are manhole covers circular instead of square or any other shape? Explain technical reasons. Google Interview Classic
The clock and its hands
Level 2 · Core · ●●○○○
How many times a day do the minute and hour hands of an analog clock overlap exactly? (Don't count the overlap at 12:00 twice)
The 100-story building and the two eggs
Level 2 · Core · ●●○○○
You have two identical eggs and access to a 100-story building. Eggs can be very resistant or very fragile. Both are identical. You need to determine the hig...
The rope around the Earth
Level 2 · Core · ●●○○○
A rope surrounds the Earth adjusted to the equator. It then elongates exactly 2\pi meters and separates itself evenly from the ground around the entire plane...
The crossing of the river (classical China)
Level 2 · Core · ●●○○○
A farmer must cross a river with a wolf, a goat and a cabbage. Your boat can only carry the farmer and one of the three elements. If you leave the wolf alone...
The Tower of Hanoi (Indian tradition)
Level 2 · Core · ●●○○○
There are three rods and a tower of n discs of different sizes, stacked from largest to smallest. You can only move one disk at a time and never put a large...
The three vessels of the wise man (ancient India)
Level 2 · Core · ●●○○○
A wise man has three clay vessels: one of 12 liters, one of 8 liters and one of 5 liters. The 12 liter vessel is filled with sacred oil. You must divide the...
The invisible submarine
Level 5 · Expert · ●●●●●
There is an infinite line of whole squares: \dots,-2,-1,0,1,2,\dots An invisible submarine has: unknown integer initial position X , unknown constant integer...