Generator

birthday

A generator in the probability library, called 4 times across 1 essays. Below: what it draws at its defaults and at each mode an essay asks for, what it checks while drawing, and everywhere it is used.

birthday is one function. Everything below came out of it during this build, at parameters taken from the essays rather than invented for this page — so a figure here is the same figure a reader meets in an essay, and if the generator changes, this page changes with it.

At its defaults

When a shared birthday becomes likelyThe chance that some pair in a group shares a birthday, against group size. It passes a half at 23 people, where the probability is 50.7%.01020304050607000.20.40.60.81people in the groupchance of a match23 people — 50.7%

show: "pairs"

The question is about pairs, not peopleGroup size against the number of pairs it contains, and the chance of a match. Doubling the people roughly quadruples the pairs, which is why the answer is so much smaller than 365.peoplepairschance of a match5102.7%104511.7%2325350.7%4078089.1%

What it checks while it draws

Collected by running the family and listening to lib/verify.js, not written here. The count is how many separate times this build put that claim to the test.

Where it is called

Changing this generator changes every figure on this list. That is what makes the list worth publishing rather than keeping in a check script.

The whole library · What the figures prove