A major source of inefficiency in barter economies is that they require a. a double coincidence of wants in exchange.
The barter system is 'inefficient' because a 'double coincidence of wants' is required. Bartering between two parties requires that both parties have what the other wants.
There is no standard unit of account/common measure of value.
Therefore, the Barter system is considered an 'inefficient' system.
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