1Two things about flipping a coin
A coin clumps — and a streak is a run in a row
You only need two ideas. Watch each one:
A coin has no memory
Every flip is a brand new 50/50. The coin doesn't know it just landed heads, and it never tries to "even out." So heads can land again and again — the flips clump up.
A run is a streak in a row
HHHH is a run of 4 heads. The longest run in a strip is its fingerprint. We're going to measure it — and it tells you more than you'd think.
2Two strips that both say "random"
The "spread it out" strip vs the "let it clump" strip
Here are two strips. They look different — but which one is the real coin and which is the person faking it?
The "spread it out" strip
Tidy and even. It keeps switching — H T H T H H — and almost never lets the same side land many times.
The "let it clump" strip
Messier. Somewhere in here is a surprising long streak of the same side — it almost looks like a pattern.
3Your turn — fake it yourself
Tap out a strip that looks random
Tap Heads and Tails to build a strip of about 40 flips — try to make it look really random, like a coin would. The meter tracks your longest run as you go.
Your "random-looking" strip
4Now run the streak detector
Your strip vs a real coin — which one hides a long streak? 🔎
On the left is the strip you just tapped out. On the right, the page just flipped a real coin 40 times. A detector will scan both and light up the longest run it finds. Guess first — then run it.
Guess before you scan
One strip is yours, tapped out to look random. One is real coin flips. Which one is hiding a long streak like HHHHHH?