The unexpected maths problem at work during the Women's World Cup

If you are in a room with 22 other people, it’s more likely than not that two of them share a birthday.

There was something strange about the recent Women's World Cup in Australia. If you were paying close attention, you might have spotted it. Many of the international teams had players who were born on the same day of the year – they shared birthdays.

What was going on?

There is a counterintuitive phenomenon known as "the birthday problem" or "the birthday paradox", which mathematicians like to use to confound our expectations. The problem is usually phrased along these lines: "How many people do you need to have at a gathering before the probability of at least two people sharing a birthday rises above 50%">window._taboola = window._taboola || []; _taboola.push({ mode: 'alternating-thumbnails-a', container: 'taboola-below-article', placement: 'Below Article', target_type: 'mix' });