One day, the teacher walks into her classroom and announces to the
 class that on each Friday, she will ask a question, and anyone who
 answers correctly doesn't have to come to school the following
 Monday. 
 
 On the first Friday, the teacher asks, "How many grains of sand
 are on the beach?" Needless to say, no one could answer. 
 
 The following Friday, the teacher asks the class, "How many  stars
 are in the sky?" And again no one could answer. 
 
 Frustrated, little Johnny decides that the next Friday, he would
 somehow answer the question and get a 3 day weekend. 
 
 So Thursday night, Johnny takes 200 Ping-Pong balls and paints
 them black. The next day, he brings them to school in a paper bag.
 At the end of the day, just when the teacher says, "Here's this
 week's question," Johnny empties the bag on the floor, sending the
 Ping-Pong balls rolling to the front of the room. 
 
 The teacher shouts, "Okay, who's the comedian with the black
 balls?" 
 
 Immediately, little Johnny stands up and yells, "Bill Cosby! 
 See ya on Tuesday!"