trade store owner solving 16-7=?

This film was taken in 1980. The man interviewed is a trade store owner who has developed new ways of using the body part counting system to solve arithmetic problems. He is presented with the problem that he has one kina and sixty toea and spends seventy toea. In the video, he represents one kina sixty toea as 16, distributing the value as shoulder (10) and wrist (6). Then from the side for which he has registered shoulder (10), he indicates that he spends the equivalent of seven or forearm (7). To solve the problem, he the "moves" the remaining body parts from the shoulder side to the side registering wrist. First he moves the elbow (8)  to the forearm (7); then the biceps (9) to the elbow (8) ; he finally moves the shoulder (10)  to the biceps (9). Biceps (9) then is the solution of the problem. In the Cultural Development of Mathematical Ideas, this approach is refered to as a "halved body" strategy. The man was not taught the approach; it's an approach that emerged as Oksapmin people engaged in novel practices of economic exchange with currency. (1980)

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