Some tourists in the Chicago Museum of Natural History are marveling at the dinosaur bones. One of them asks the guard, "Can you tell me how old the dinosaur bones are?"

The guard replies, "Sure. They're sixty-five million, four years, and six months old."

"That's an awfully exact number," says the tourist. "How do you know their age so precisely?"

The guard answers, "Well, they were sixty-five million years old when I started working here, and that was four and a half years ago."