A policeman pulled over a car and approached the door. He glanced at the car and saw that there were two old ladies sitting in the back, and one old lady driving. "Ma'am," he said, "it seems that you were going 15 on an interstate. The minimum speed is 40."
"Ohh, dear," said the woman. "But the sign says that it's 15!"
The policeman shook his head. "No, ma'am, it says 40."
"Ohhh, but look!" she said, pointing.
"Oh, yes, that is the number of the highway. This is highway 15."
"I understand now! I apologize, I didn't know," she answered.
"That's all right. I'll let you off this time. Drive safely." He turned around to go back to his car and notice the two ladies had petrified, frozen-in-place looks on their faces. He turned back. "Ma'am, are they all right?"
"Oh, yes, they're fine. We just turned off Highway 110."