What is the Yoruba number system?

Answer 1

See the related links for a complete description of this system and a project to better understand it and use it.

In her book, Africa Counts, Claudia Zaslavsky describes the Yoruba number system as a complex system based on 20 (vigesimal) that uses subtraction to express numbers. For example,

35 = (2 x 20) - 5; 47 = (3 x 20) - 10 - 3; 51 = (3 x 20) - 10 + 1;

According to the Yoruba system, the numbers from 1 to 10 have unique names. The numbers 11, 12, 13, and 14 are written additively (i.e., 11 = 10 + 1, 12 = 10 + 2, 13 = 10 + 3, 14 = 10 + 4). But the numbers from 15 through 19 are written using subtraction from 20. This same pattern continues for the 20s etc.

20 = ogun; 40 = ogun meji; 200 = igba; 400 = irinwo.