‘But you’re Muggles!’ said Mr Weasley delightedly. ‘We must have a drink! What’s that you’ve got there? Oh, you’re changing Muggle money. Molly, look!’ He pointed excitedly at the ten-pound notes in Mr Granger’s hand.
Chamber of Secrets - page 47 - UK Hardcover - chapter 4, Flourish and Blotts
So Gringotts exchanges Muggle money for Wizarding money. What do the Goblins do with the Muggle money after the exchange has been made? Is it possible they keep a stash of Muggle money on hand for reverse exchange purposes, or do they surreptitiously feed the money back into the Muggle economy?
What do Goblins do with Muggle money?