At a boat-rental concession, the manager went to the lake's edge and yelled through his megaphone, "Number 99, come in, please. Your time is up." Several minutes passed, but the boat didn't return. "Boat number 99," he again hollered, "return to the dock immediately or I'll have to charge you overtime."

"Something is wrong here, boss," his assistant said. "We only have 75 boats. There is no number 99."

The manager thought for a moment and then raised his mega-phone: "Boat number 66," he yelled. "Are you having trouble out there?"