William put up his hand.

"Yes, William," said the teacher. "Is there something about the sum you don't understand?"

"Please, sir," said William. "Is the answer 23?"

The teacher was very, absolutely, totally, completely amazed.

"How did you work out the sum so quickly?" he gasped. "It's impossible!"

"Nothing is impossible," said Mr. Impossible from the back of the class, and stood up.

"Well I never did," exclaimed the teacher.