Math Past Yoruba Counting Words Where do number words come from? Do other people use different words to represent numbers? What do other people’s number words mean? Write the word nineteen and ask students why they think we use that word to mean 1 ten and 9 ones. It may help to add space between nine and teen, or to underline the two parts of the word as you read it. Students should point out that the word nine is in nineteen. Some may notice that teen kind of looks and sounds like ten. In the first four modules, students learned how different people have represented and written numbers throughout history. The ways we write numbers can affect our number sense and the kinds of calculations we can perform. For example, adding and subtracting with Roman numerals is notoriously difficult! The words we use for numbers are also connected to our number sense. The connection between words and number sense is deep. We learn the words for numbers before we learn to write them, and words for numbers developed earlier in human history than written numerals, since spoken language developed first. Tell the class you met someone who says that where they grew up, they say “5 before 20” to describe a number. Ask students what number they think this person is describing. A number path can be used to help students answer this question.
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Tell the class that this is how the Yoruba people of western Africa describe the number 15. The Yoruba people form a large ethnic group, and the Yoruba language is the native language of between 30 and 40 million people! In addition to having deep mathematical traditions dating back centuries, they are also famous for their music, which features advanced drumming techniques. Unlike our decimal or base-10 system, the Yoruba number system is a vigesimal, or base-20 system. Many people in different regions of western Africa use base-20 systems, and they are used in the Americas too. For example, the Maya system, which we saw in modules 3 and 4, is also a base-20 system. The different and interesting aspect of the Yoruba system is its reliance on subtraction. Remind students how we use tens to make our numbers, making as many groups of 10 as we can, and then saying how many ones are left. Ask students why they think we use 10 this way. Hint: What do most people have 10 of that you can use to count? Fingers! When counting from 10 to 20 in Yoruba, the number words start out with a similar meaning to ours. They also describe 10 and some ones, which can be roughly translated as follows. 11
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13
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1 past 10
2 past 10
3 past 10
4 past 10
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