4-4=?

One day, the teacher inquired Peter: "How much is four minus four?" Peter was tongue-tied.

the teacher got angry and said: "What a fool! You see, if I put four coins in your pocket, but there is a hole in your pocket and all of them leak out, now what is left in your pocket?"

"The hole," replied Peter.

四减四等于几？

一天，都是问彼德：“四减四等于几？”彼德张口结舌答不上来。

老师生气地说：“真笨！你想，如果我放四个硬币在你的口袋里，但你的口袋里有个窟窿，结果四个硬币都漏掉了。那么，你的口袋里还有什么？”

“窟窿，”彼德答道。