20 (number)

20 was a number.

As a defence mechanism for the Doctor's TARDIS there were twenty wrong holes within the lock and one right one. Attempting to open the door through a wrong one would cause the lock to melt, preventing access entirely. (TV: The Daleks)

The Argolin-Foamasi War lasted twenty minutes. (TV: The Leisure Hive)

The Tenth Doctor made the observation to Richard Lazarus that some people lived more in twenty years than others did in eighty. (TV: The Lazarus Experiment)

The fruit flies of Hoppledom Six had a lifespan of only twenty minutes. (TV: The Pandorica Opens)

A notice in the window of a shop in Queen's Arcade offered "20% off" of products. (TV: Rose)

Vivien Rook met Lucy Saxon at 10 Downing Street, ostensibly to request a 20 minute interview for a front page profile piece on "Britain's First Lady" and "The Power Behind the Throne". In reality, however, this was a ruse for Vivien to bring her findings on Harold Saxon to his wife. Lucy, fully aware that her husband was, accepted a 20 minute interview only to leave Vivien to be killed by the Toclafane. (TV: The Sound of Drums)

Room 12, a room within the Twelfth Doctor's confession dial, contained a portal to Gallifrey that was behind a 20 foot thick azbantium wall. (TV: Heaven Sent) Chronon, (WC: 14682 UNIT Field Log, 14683 UNIT Field Log, 14684 UNIT Field Log) or cronon (WC: 14681 UNIT Field Log) and artron energy readings during the recording of UNIT field logs included 17%, (WC: 14682 UNIT Field Log) 18%, 19%, (WC: 14681 UNIT Field Log, 14682 UNIT Field Log) 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, (WC: 14682 UNIT Field Log) 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, (WC: 14682 UNIT Field Log, 14684 UNIT Field Log) 90%, (WC: 14682 UNIT Field Log, 14683 UNIT Field Log) 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, 101%, 102%, 103%, 104%, 105%, 106%, and, in the case of Chronon energy, 107%. (WC: 14683 UNIT Field Log)

Behind the scenes
According to The Last Dalek, a video game based on the events of the television episode Dalek, Adam Mitchell was 20 years old in 2012.