Step-by-step visual solutions

Brain Puzzles

Logic, math, everyday and lateral-thinking riddles — each one paired with a step-by-step visual walkthrough of the solution, right in your browser.

36puzzles

4categories

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Wolf, Goat & Cabbage

Ferry a wolf, a goat and a cabbage across a river without ever leaving a predator alone with its prey.

Easy

Knights & Knaves

On an island of truth-tellers and liars, one islander's claim is enough to deduce everyone's nature.

Medium

The Mutilated Chessboard

Two opposite corners are cut off. Can 31 dominoes still tile the board?

Medium

Three Light Switches

One of three switches controls a hidden bulb. Identify it with a single visit to the room.

Easy

The 3×3 Latin Square

Fill a 3×3 grid so each row and column contains 1, 2 and 3 — pure elimination.

Easy

The Game of Nim

Three piles of stones and a winning strategy hidden in binary XOR.

Hard

Two Guards, One Question

One guard always lies, one always tells the truth. Find the safe door with a single question.

Medium

The Mislabeled Boxes

Three boxes, every label wrong. Fix all of them by drawing just one fruit.

Medium

Cheryl's Birthday

Two friends know only the month or the day. Their conversation reveals the date.

Hard

Tower of Hanoi

Move a stack of disks to another peg, one at a time, never resting a larger disk on a smaller one.

Medium

What Comes Next?

Spot the hidden rule behind 2, 6, 12, 20, 30 and predict the next term.

Easy

The Bat and Ball

A bat and ball cost $1.10; the bat costs $1 more. The obvious answer is wrong.

Easy

Gauss's Sum

Add 1 to 100 in seconds — the trick a young Gauss reputedly found in class.

Easy

Rice on a Chessboard

One grain on the first square, doubling each square. How much rice by the 64th?

Medium

The Handshake Problem

If everyone in a room of six shakes hands once, how many handshakes happen?

Easy

Fibonacci's Rabbits

1, 1, 2, 3, 5, 8, 13 … the sequence that models breeding rabbits — and appears everywhere.

Medium

Odd Numbers Make Squares

Why does 1 + 3 + 5 + 7 + … always land on a perfect square? See it, don't prove it.

Easy

The Missing Dollar

$27 paid, $2 kept — that's $29. So where is the thirtieth dollar?

Medium

The Water Jug Problem

Measure exactly four litres with only a five-litre and a three-litre jug.

Medium

Bridge & Torch

Get four people with different speeds across a night bridge, sharing one torch, in the least time.

Hard

The Burning Ropes

Two ropes, each burning an hour but unevenly. Measure exactly 45 minutes.

Medium

Socks in the Dark

Blue and black socks jumbled in a drawer. How many grabs guarantee a matching pair?

Easy

The Camel and Bananas

A camel hauls bananas to market but eats them as it walks. How many survive the trip?

Hard

The Poisoned Wine

One of eight bottles is poisoned. Three tasters and binary code find it in one day.

Hard

The Two-Egg Drop

Find the highest safe floor in a 100-storey building with just two eggs — in as few drops as possible.

Hard

The 100 Lockers

100 lockers, 100 passes of toggling. Which ones end up open?

Medium

The Monk on the Mountain

A monk climbs up one day and down the next. Is there a spot he passes at the same time both days?

Medium

The Counterfeit Coin

One of eight coins is heavier. Pin it down with only two turns of a balance scale.

Hard

The Monty Hall Problem

A game show, three doors, and a counter-intuitive truth: switching doubles your odds.

Medium

The Pirates' Gold

Five ruthless pirates split 100 coins by vote. How much can the captain keep?

Hard

The Twelve Coins

Scale the counterfeit-coin hunt to twelve coins — still just three weighings.

Hard

The Prisoners' Hats

A line of prisoners in red or blue hats. One clever signal saves almost everyone.

Hard

The Birthday Paradox

How few people does it take for two to share a birthday? Far fewer than you'd think.

Medium

The Wason Selection Task

Four cards, one logical rule, and the classic trap of confirming instead of falsifying.

Medium

The Boy or Girl Paradox

A family has two kids, at least one a boy. The chance both are boys isn't ½.

Hard

The Prisoner's Dilemma

Two suspects, one choice each. Why rational self-interest lands both in worse cells.

Medium

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