Puzzle
Archive
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?