"How To Correctly Date Dinosaur Bones"

Some tourists in the 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, "They are three 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, the dinosaur bones
were three million years old when I started working
here, and that was four and a half years ago."