Miss Jones teaches at a school. She teaches the boys and girls about nine years old. The pupils are not good at maths in one of her classes. Miss Jones always wants to make her lessons interesting.
One day she gave them a question. "If you go to the shop to buy apples," she said, "and an apple and a half cost twelve cents (美分), how much will you have to give for twelve apples?"
The pupils began to write in their exercise books, and for a long time nobody spoke. Then one boy put his hand up and said, "Could you say the question once again, please?" Miss Jones said, "If an apple and a half..." But the boy shouted, "oh, an apple and a half? All the time I am working it out (算出来) in oranges, Miss Jones. So the answer must be different."