flip 10 coinsFlip 10 coins

Flip ten coins at once

Ten coins in one throw, for experiments that would take ages one flip at a time. Tap the coins, press Flip or hit the Space bar. The result shows how many heads and tails landed, and the bar at the bottom totals every coin since your last Reset.

Five and five is not the usual result

The natural guess for ten fair coins is five heads and five tails. It is indeed the single most likely result, but it only happens about a quarter of the time, 24.6%. In three flips out of four, the split is something else. What is likely is a result close to half: between four and six heads about 66% of the time. Eight heads or more happens about 5.5% of the time, so it will turn up if you flip often enough.

Streaks are normal

Read the ten coins from left to right as a sequence. You will often see three or four of the same face in a row: a run of at least four identical faces appears in about 46% of throws, and a run of at least three in about 83%. When people invent random sequences by hand, they tend to switch too often and avoid streaks. Teachers use this to tell real coin records from made-up ones.

The law of large numbers, live

• Flip ten times and watch the running tally at the bottom. With 100 coins counted, the share of heads can still be some way from 50%.
• Keep going to 500 or 1,000 coins: the share settles closer to half, even though the gap between heads and tails, in absolute numbers, can still grow.
• The history keeps your recent results, so you can note them for a class chart.