Hard
Requires specific techniques like induction, graph theory, or advanced proofs. Multiple interconnected insights needed.
Treasure and Locks
Thirteen pirates put their treasure in a chest. They want the chest to be openable whenever a majority of them (7 or more) agree, but not when only a minority...
Stack of Coins 3
Once more, you and your friend stumble on another pirate’s treasure: an old chest filled with coins: 575 copper coins and 1 gold coin. As before, these old...
Jewel Thieves and a Stolen Gem
The Moonstone has been stolen. Police have three suspects under surveillance—three of the city’s most notorious jewel thieves—but no evidence to arrest any of...
Ant on a Rubber Band
A taut rubber band connects a wall to the back of a toy racecar 1 metre away. At time t = 0 , the racecar drives away from the wall at 1 metre per second,...
3-Bit Sensors
A remote weather station uses two redundant 3-bit sensors to measure atmospheric pressure. Both sensors transmit their readings to a central processor, but...
Chomp 4
After beating your friend at his game 3 times already, you wonder if there’s always a way to win for an n by m chocolate bar. As a reminder, here are the rules...
Traversing the Hypercube
Ossarion-429 is a multi-dimensional being travelling across hypercubes of various dimensions. Bored and having nothing else to do, he wonders to himself if...
Average Salaries 2
Back in [[puzzle ]], 12 employees came up with a method to find out their average salary without revealing their individual salaries to anyone. Here’s the...