Little Donald was being questioned by the teacher during an arithmetic lesson.
"If you had 100 naira," said the teacher, "and I asked you for a loan of 80 naira, how much would you have left?"
"100," said Little Donald firmly.
"100?" the teacher said, "How do you get it 100?"
"Well," replied Little Donald, "You may ask for a loan of 80 naira, but that doesn't mean I will give it to you!"