The nomadic mongol people traded wool for the wood they needed to make frames for shelter. this is an example of what system?

   Barter system

Explanation:  Barter is a system of trade in which goods are exchanged directly for other goods, so there is no use of any medium of exchange such as money and other securities etc. It is one of the oldest methods of trade where services could be exchanged in addition to goods. Of course, in the barter system, the participants negotiated the exchange of the amount of goods that would be exchanged, so the price.