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Find the main idea from the following passage: dumb bartering took place in this way: Their donkeys ladened with grains, leather, cloth, salt, traders arrived at Wangara, where men lived in holes. There traders spread out their goods along a stream or near a thicket. Then they announced their presence by beating on a drum. The merchants went away. The shy Wangaran miners crept from their hiding places and laid out a measure of gold dust.
What is dumb bartering.