Puzzle
Archive
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?
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?
Elevator Probability
You enter a building with 12 floors and press your floor at random. What is the expected number of stops if 3 other passengers do the same?