Swapping dollars enriches nobody but swapping ideas enriches both parties to the trade.
A noted wag met an Irishman in the street one day, and thought he would be funny at his expense.
"Hello, Pat!" he said. "I'll give you eight (in) pence for a shilling."
"Will ye, now?" said Pat.
"Yes," he replied.
The Irishman handed over the shilling, and his friend put eight pence into his palm in return.
"Eight in pence," he explained. "Not bad, is it?"
"No," answered Pat; "but the shilling is!"