20 (number) – Wikipedia

Natural number

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20 (twenty; Roman numeral XX) is the natural number following 19 and preceding 21. A group of twenty units may also be referred to as a score.^[1][2]

In mathematics[edit]

In science[edit]

Biology[edit]

• The number of proteinogenic amino acids that are encoded by the standard genetic code.
• In some countries, the number 20 is used as an index in measuring visual acuity. 20/20 indicates normal vision at 20 feet, although it is commonly used to mean “perfect vision”. (Note that this applies only to countries using the Imperial system. The metric equivalent is 6/6.) When someone is able to see only after an event how things turned out, that person is often said to have had “20/20 hindsight”.^[12]

As an indefinite number[edit]

• A ‘score’ is a group of 20 (often used in combination with a cardinal number, i.e. fourscore to mean 80),^[13] but also often used as an indefinite number^[14] (e.g. the newspaper headline “Scores of Typhoon Survivors Flown to Manila”).^[15]

In sports[edit]

In other fields[edit]

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