This is an old joke...I have tried to clean it up as much as possible without losing the humor. I apologize if anyone is offended.
Setting: Early 1920s in a rural country school.
In order to graduate from the eighth grade after many previous failed-attempts, Stu Dent needs to pass a math competency test.
"Here's your first question," the teacher said. "Without using numbers, represent the number 9."
"Withouta numbers?" Stu says, "Datsa easy." and he proceeds to draw three trees.
"What's this?" the teacher asks.
"Ave you gota no brain? Tree and tree and tree makes a nine," says Stu.
"Fair enough,' says the teacher. "Here's your second question. Use the same rules, but this time the number is 99."
Stu stares into space for a while, then picks up the picture that he has just drawn and makes a smudge on each tree . "Ere you go."
The teacher scratches her head and says, "How on earth do you get that to represent 99?"
"Eacha of da trees is a dirty now. So, it's dirty tree, and dirty tree, and dirty tree. Datsa a 99."
The teacher is getting worried that Stu is actually going to pass test this year, so she says, "All right, last question. Same rules again, but represent the number 100."
Stu stares into space some more, then picks up the picture again and makes a little mark at the base of each tree and says, "Ere you go.
The teacher looks at the attempt. 'You must be mistaken if you think that represents a hundred!"
Stu leans forward and points to the marks at the base of each tree and says, "A little doga come along and poops byeacha tree. So now you gota dirty tree and a turd, dirty tree and a turd, and dirty tree and a turd, data makea one hundred. So, do I graduate?"