HOW OLD ?

Some tourists in a Museum of Natural History were marveling at the dinosaur bones. One of them asked the guard, Pappu : "Can you tell me how old the dinosaur bones are?"

Pappu replied : "They are 3 million, four years, and six months old"

"That's an awfully exact number" says the tourist.

"How do you know their age so precisely?"

Pappu answered "Well, the dinosaur bones were three million years old when I started working here, and that was four and a half years ago