Friday Puzzler -- Counterfeit
Alex Y
Ann goes to Bob's stall in a flea market, and haggles over the price of a vase. Bob finally decides to sell it to her at his cost--$20. Ann pays with a $100 bill. Bob doesn't have change for the $100 in his cash drawer, so he asks Charlie in the next booth if he can break a $100. He can, and gives Bob five $20s. Bob gives Ann four of them as change, and puts the fifth in his cash drawer. As soon as Ann has left, Charlie comes over and says that the $100 is a counterfeit. Bob examines it, agrees, and takes back the bad $100, giving Charlie a good one from his cash drawer.
How much did Bob lose in these transactions?