Puzzle
Archive
Four Squares, One Lock
Four 3×3 grids, each a Latin square on 1, 2 and 3. Two carry a sum clue, two a product clue, and four small letters tie cells together across the squares. Solve all four, read the center numbers in order, and the lock opens. You get three tries, and the lock keeps count.
The Petri Dish Problem
A petri dish of bacteria doubles every minute and is full at noon. When was it half full? This deceptively simple riddle reveals the surprising power—and danger—of exponential growth.
Does the 37% Rule Really Work?
How do you choose the very best when choices appear one by one and there’s no going back? Kepler wrestled with this centuries ago. The answer is a surprisingly simple strategy with odds so powerful it became known as the 37% rule.
The Fourth-Power Faucet
Two straws. Same milkshake. Same effort. One straw is twice as wide. How much more do you drink? The answer is far bigger than intuition suggests—and reveals a hidden law that governs everything from arteries to garden hoses.
Eight Fair Slices
Eight equal slices that look nothing alike, one 7-inch mark. How big is the triangle?
Too Even to Be Random
A teacher catches the students who faked their coin flips with one rule. Real randomness is lumpier than you think.
The Cards That Count for Nothing... Or Do They?
Card counting squeezes a whole shoe into one number — and the famous Hi-Lo system scores three of the thirteen ranks as a flat zero. Wasteful? We test whether folding the 7, 8 and 9 back in builds a sharper count, and find that doing *less* wins.
The Pen That Cried Wolf
A counterfeit-detector pen is 99% accurate at catching fakes and almost never misfires. It just flagged a customer's $100 bill. So why is the bill still almost certainly real?
Up Like a Rocket, Down Like a Feather
Five price signals, five right triangles, one angle that tells you when the (asset) rocket is too vertical to stay aloft. A trader's intuition expressed in tangents.
The Farmer’s Impossible-Looking Receipt
A farmer buys 10,000 young animals at market: calves, lambs, and piglets. The receipt totals $505,000, the lambs outnumber calves three-to-one, and the piglets arrive in tidy hundreds. Can you reconstruct the herd?
Ride-sharing: What the Wait Time Tells You
An 8-minute wait sounds like evidence of surge pricing. The math says otherwise: it barely shifts your estimate from the prior. Using exponential wait-time distributions, Bayes' theorem, and simple cost-benefit analysis, this puzzle explores why observed data can be surprisingly uninformative.
How Big Is Half a Lottery?
A $1 billion jackpot. Seven numbers, drawn with replacement from 1–19. You want a 50% chance of winning. How many $1 tickets must you buy — and will it ever be worth it?