In a room of just 23 random people, the chance that two share a birthday is better than even. The reason is that people compare birthdays in every pair, not just with a fixed person. Twenty-three people make 253 distinct pairs, and each pair offers a chance of a match, so the odds add up fast. With 70 people the chance rises above 99.9 percent, even though there are 365 possible birthdays. The result is a veridical paradox: it feels wrong but is mathematically true. The problem was attributed to Harold Davenport around 1927, and Richard von Mises published a version in 1939.
how it works
The number of pairs grows much faster than the number of people, since n people form n(n-1)/2 pairs. Each pair has about a 1 in 365 chance of matching, and the chances across all pairs combine, so the probability of at least one match climbs quickly.
so what
The birthday problem shows why coincidences are far less rare than intuition suggests, which matters for everything from statistics to security. It also explains why people overestimate how unusual shared events are.
From Wikipedia, the free encyclopedia · text CC BY-SA 4.0
Illustrative photo · Rajkiran g, CC BY-SA 3.0, via Wikimedia Commons
In 1909 D. W. Griffith made a 14-minute film about a speculator who corners the wheat market and doubles the price of bread. A farmer sows his field while a 'Wheat King' gambles in the Chicago wheat pit; bakers raise the loaf from five cents to ten and the poor line up for bread. Griffith cut back and forth between the farm, the feast and the breadline, a technique called parallel editing, so audiences saw both ends of the economy at once. The film drew on Frank Norris's stories and on a real scheme: months earlier Chicago financier James Patten had cornered wheat, sent bread prices up and made about $5 million, roughly $185 million today.
how it works
To corner a market, a trader buys up most of the available supply and the futures contracts that promise more. Anyone who has to deliver the commodity must then buy from the cornerer at whatever price is demanded. The trader profits until the stock is released or the scheme collapses.
so what
A century on, it still shows how markets can be rigged by someone who controls supply, and how the people at either end, farmers and eaters, pay for it. It also helped establish editing as a way to argue a point, not just tell a story.
the bigger pattern
Corners have recurred whenever supply could be locked up, from the Hunt brothers' attempt on silver in 1979 to 1980 to the 'Black Friday' gold panic of 1869. Many such schemes end by collapsing, and the response is often new rules on speculation.
fun fact
In the film the Wheat King dies by falling into a grain elevator and being buried in the wheat he hoarded, an ending borrowed from Norris's novel The Octopus.
more on this
background
A Corner in Wheat is a 1909 American short silent film which tells of a greedy tycoon who tries to corner the market in wheat, destroying the lives of the people who can no longer afford to buy bread. It was directed by D. W. Griffith and adapted by Griffith and Frank E. Woods from a novel and a short story by Frank Norris, titled The Pit and "A Deal in Wheat". Griffith may have had a real-life inspiration: six months earlier, James A. Patten had actually cornered the market in wheat, and in some cities, the price of bread doubled from five cents to ten, just as in the movie.
In 1994, A Corner in Wheat was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant".
Usman Khawaja refuses to answer Sandpapergate question about Pat Cummins | 7.30
from ABC News In-depth
One of the darkest days in Australia's sporting history has been dragged back into the spotlight.
A new autobiography by former Test cricketer Usman Khawaja has made explosive revelations about the Australian Test team's 2018 ball-tampering saga in South Africa.
7.30 host Sarah Ferguson speaks to Usman Khawaja.
7.30 is the ABC's flagship current affairs program, delivering original journalism, exclusive investigations, in-depth analysis and interviews on the major issues affecting Australia and the world.
With on-the-ground reporting from ABC journalists across every state and territory and around the world, 7.30 has the latest on politics, policy, the economy, cost of living, housing, health, climate and energy, national security and global affairs.
Note: In most cases, our captions are auto-generated.
