Vigesimal
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A vigesimal numeral system has a base of twenty.
Twenty (vingt) is used as a base number in French. E.g. quatre-vingts means 4 times 20, i.e. 80.
Twenty (tyve) is used as a base number in the Danish language: Tres (short for tresindstyve) means 3 times 20, i.e. 60; firs (short for firsindstyve) means 4 times 20 i.e. 80. halvtreds means (3 - 1/2) times 20, i.e. 50; halvfjerds means (4 - 1/2) times 20, i.e. 70; and halvfems means (5 - 1/2) times 20, i.e. 90.
Twenty (ugain) is used as a base number in the Welsh language, although in the latter part of the twentieth century a decimal counting system came to be preferred, with the vigesimal system becoming 'traditional'. Deugain means 2 times 20 i.e. 40, trigain means 3 times 20 i.e. 60. Prior to the currency decimalisation in 1971, papur chwigain (6 times 20 paper) was the nickname for the 10 shilling (=120 pence) note.
Twenty (otsi) is used as a base number in the Georgian language. For example, 31 (otsdatertmet'i) literally means, twenty-and-eleven. 67 (samotsdashvidi) is said as, "three-twenty-and-seven."
Twenty may have been the base of the Maya and Aztec number system, see Maya numerals and Maya calendar.
In the old British currency system, there were twenty shillings in a pound.
In English, counting by the score has been used historically, as in the famous opening of the Gettysburg Address "Four score and seven years ago...", meaning eighty-seven years ago. This method has fallen into disuse, however.
According to German linguist Theo Vennemann, the vigesimal system in Europe is of Basque (Vasconic) origin and spread from the Vasconic languages to other European tongues, such as many Celtic languages, French and Danish.
However according to Menninger the vigesimal system originated with the Normans and spread through them to Western Europe.
Further reading
- Karl Menninger: Number words and number symbols: a cultural history of numbers; translated by Paul Broneer from the revised German edition. Cambridge, Mass.: M.I.T. Press, 1969 (also available in paperback: New York: Dover, 1992 ISBN 0-486-27096-3)de:Vigesimalsystem