The archive
Paradoxes & riddles.
The kind of math that isn't a problem to solve — it's a trap to watch spring. Free to watch, any time.
The films
Longer stories, a few minutes each.
1:16The Barber's Paradox
Russell's Paradox in everyday clothes
1:32The Banach–Tarski Paradox
one ball becomes two
1:51Hilbert's Hotel
infinitely many rooms, all full
1:13Zeno's Paradox: Achilles and the Tortoise
the race that logic says never ends
1:38The Two Envelope Paradox
a small calculation, an impossible conclusion
1:05Ants on a Ruler
a puzzle with a clever shortcut
1:34The Blue Eyes Puzzle
a logic puzzle about common knowledge
Quick paradoxes & riddles
78 short videos, about a minute and a half each.
1:40The Bat and Ball Riddle
an easy question most people get wrong
1:45The Berry Paradox
a number too hard to describe?
1:36Bertrand's Box Paradox
gold coin, gold box?
1:38The Birthday Paradox
how many people until two share a birthday?
1:49Braess's Paradox
when a new road makes traffic worse
1:41The Bridge and Torch Riddle
four people, one torch, 17 minutes
1:28The Burning Ropes Riddle
measure 45 minutes with two ropes
1:35The Cake in Three Cuts
8 pieces, 3 straight cuts
1:44The Census Taker's Riddle
how old are the three children?
1:46Cheryl's Birthday
the logic puzzle that went viral
1:39How Many Squares on a Chessboard?
the answer isn't 64
1:45Chickens and Rabbits
count the heads, count the legs
1:31The Class Size Paradox
why your classes feel bigger than average
1:32The Clock Hands Riddle
how often do the hands overlap?
1:35The Coastline Paradox
how long is a coastline?
1:39The Coin Rotation Paradox
how many times does it turn?
1:38Counting the Ones
how many 1s from 1 to 100?
1:47Cutting a Cube Into 27
can you do it in fewer than 6 cuts?
1:50De Méré's Dice Problem
the gamble that started probability
1:55The Nines Trick
why digit sums reveal remainders
1:36The Doubling Penny
a penny a day, doubled, for 30 days
1:32A Fair Coin From an Unfair One
the two-flip trick
1:45The Fake Coin Stacks
find the fake stack in 1 weighing
1:46The False Positive Paradox
when a positive test is probably wrong
1:50The 15 Puzzle
the swap that can't be done
1:41The Fly Between Two Trains
the hard way and the easy way
1:39The Four Color Theorem
how many colors does a map need?
1:47The Friendship Paradox
why your friends have more friends than you
1:45Gabriel's Horn
fill it with paint, but never paint it
1:49Galileo's Paradox
are there as many squares as numbers?
1:45The Gambler's Fallacy
is heads 'due' after a streak?
1:36The Game of 21
the winning strategy
1:31Adding 1 to 100
the shortcut a schoolboy found
1:38The Handshake Problem
how many handshakes in a room?
1:37The Head Start Race
a 10 meter handicap
1:27The Heavy Ball Riddle
find the heavy one in 2 weighings
1:35The 25 Horses Puzzle
find the fastest 3 in 7 races
1:53The Two Hourglasses Riddle
measure 9 minutes with a 4 and a 7
1:50The 100 Lockers Riddle
which lockers end up open?
1:43Why Primes Never Run Out
Euclid's proof
1:47The Interesting Number Paradox
is every number interesting?
1:34The Josephus Circle
who is left standing?
1:39Knights and Knaves
who is lying?
1:42The Leap Year Rule
why 2000 was a leap year but 1900 wasn't
1:27The Liar Paradox
this sentence is false
1:18The Lily Pad Riddle
the power of doubling
1:31The Missing Dollar Riddle
where did the dollar go?
1:43The Monk on the Mountain
the same place at the same time
1:37The Monty Hall Problem
should you switch doors?
1:40The Mutilated Chessboard
can dominoes cover it?
1:41The Pizza Size Riddle
one big pizza or two small ones?
1:47Does 0.999... Equal 1?
an endless decimal with a surprising value
1:33The Potato Paradox
a tiny change in water, half the weight
1:40Rice on a Chessboard
the power of doubling, square by square
1:30The River Crossing Riddle
a wolf, a goat, and a cabbage
1:48Why the Square Root of 2 Isn't a Fraction
a proof by contradiction
1:42The Rope Around the Earth
how much rope to lift it 1 meter?
1:54The Seven Bridges of Königsberg
the walk that can't be done
1:44The Seventeen Camels
the borrowed camel riddle
1:47The Ship of Theseus
is it still the same ship?
1:56Simpson's Paradox
winning every group, losing overall
1:37The Snail in the Well
why it isn't 30 days
1:33The Sock Drawer Riddle
how many socks for a matching pair?
1:47The Heap Paradox
when does a heap stop being a heap?
1:45The Spoiled Juice Bottles
1,000 bottles, 10 tasters
1:42The St. Petersburg Paradox
a game worth infinite money?
1:38Adding Up Odd Numbers
why the sums are always squares
1:25Survivorship Bias
the missing bullet holes
1:43Splitting 8 Liters Evenly
an 8, a 5 and a 3 liter jug
1:41The Three Prisoners Problem
what did the warden really tell you?
1:42The Three Light Switches Riddle
one bulb, one look
1:49The Tower of Hanoi
the puzzle that would take 585 billion years
1:42The Two Eggs Puzzle
100 floors, 2 eggs, fewest drops
1:36The Two Guards Riddle
one always lies, one always tells the truth
1:28The Water Jugs Riddle
measure 4 liters with a 3 and a 5
1:48The Will Rogers Phenomenon
both averages go up, nobody changes
1:33The Wine and Water Puzzle
which glass is more mixed?
1:49Why 0! Equals 1
the factorial of nothing