The teacher noticed that Susie had been daydreaming for a long time, so she decided to get her attention.
"Susie," she said, "if the world is 25,000 miles around and eggs are sixty cents a dozen, how old am I?"
Without hesitation, Susie answered, "Thirty-four."
The teacher replied, "Well, that's not far from my actual age. Tell me ... how did you guess?"
"Oh, there's nothing to it," Susie said. "My big sister is seventeen and she's only half-crazy."