Brain Teasers
Brain teasers are the catch-all for puzzles that reward a moment of insight rather than a methodical derivation — the kind where the trick, once seen, makes the rest obvious. They don't require the yes/no interrogation of a lateral-thinking puzzle or the wordplay of a riddle; they're closer to a compact "aha" problem.
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The Ferryman’s Troublesome Cargo
A traveller reaches a river with three awkward pieces of cargo: a wolf, a goat, and a basket of cabbages. His small boat can carry only the traveller and one of them at a time. He may also cross alone. Whenever the trave…
The Expanding Lily
A single water lily is growing across a quiet pond. Each day, the total surface area covered by the lily becomes exactly twice what it covered the day before. The growth continues at this steady rate, and at the end of t…
The Traveling Spoonful
Two glasses sit on a table. One contains only water, and the other contains only wine. A full spoonful is taken from the wine glass, poured into the water glass, and stirred until the liquids are evenly mixed. Next, usin…
The Warden’s Unmarked Morning
At noon on Sunday, a judge tells a prisoner: “On exactly one weekday next week, you will be taken to the courtyard and hanged. The date will not be announced beforehand, and when you wake that morning you will not be abl…
The Fly’s Final Commute
Two trains are travelling toward each other along the same straight track. At the start, the fronts of the trains are 120 kilometres apart, and each train moves at a constant speed of 40 kilometres per hour. A fly begins…
The Four-Litre Finish
You have two unmarked jugs. One holds exactly three litres, and the other holds exactly five litres. A water supply and a drain are both available, so you may use as much water as needed. Each of the following actions c…
The Last Question at the Gate
You stand in a stone chamber with two closed doors. One door leads safely outside; the other opens onto a fatal trap. A guard stands beside each door. Both guards know which exit is safe. One guard always speaks truthful…
The Counterfeit Dozen
Twelve coins are visually indistinguishable. Eleven have exactly the same weight; the remaining coin is either heavier or lighter, but you do not know which. You have a two-pan balance scale that reports only whether the…
The Eight-Disc Transfer
A tower of eight discs rests on the left peg. Every disc has a different diameter, and the discs are arranged from largest at the bottom to smallest at the top. Two other pegs stand empty. Your task is to rebuild the ent…
The Dark Door Test
A closed room contains one working incandescent bulb. Outside the room are three switches, labeled A, B, and C. Exactly one switch controls the bulb; the other two are disconnected. The door is sealed well enough that yo…
The Third Sage Speaks
Three sages are shown a collection of five hats: three are white and two are black. While their eyes are closed, each sage is given one hat to wear. The two unused hats are hidden. Once they open their eyes, each sage c…
A Pair in the Dark
A bedroom drawer contains a jumble of socks in exactly two colors: black and blue. There are plenty of socks of each color, but the room is completely dark, so you cannot tell one color from the other by looking. You mus…
This is a curated collection, not a solver-verified one — brain teasers don't reduce to the kind of constraint-satisfaction problem the site's logic grids, zebra puzzles, and knights-&-knaves puzzles are checked against, so they carry no ∎ badge. Each card shows whether it's a reviewed puzzle or an unreviewed import.