There once was a famous professor, who always wrote the number 2 and 4 on the blackboard at the first course to his new students, and asked the students what is the answer.
一位非常著名的教授，每次給新生上第一堂課時，總是在黑板上寫下“2”和“4”兩個數字，然后轉過身問學生：“答案是什么?”

Every time when he asked this question, some of his students said 6 is the key while some others hold that 2 is more proper and some of them chose 8 as the answer, moreover, there were still others who were just sitting at their seats without a word.
　 有的同學說是“6”，有的同學說是“2”，還有的說是“8”。其他的一些人感覺無聊，坐在那里一言不發。

But at the time that the students were discussing the issues, the professor always sighed and said to the students “It is no use for you to debate because all of you did not focused the key point: what exactly the question is asked about? Do those two numbers were being to be added, subtracted or be acquired to do some other calculations? Without what the question is exactly about, how can you make a right respond”.
　 就在大家議論紛紛的時候，教授嘆著氣對學生們說：“你們爭論是沒有用的，因為你們都沒有注意到一個關鍵的問題：這個問題到底在問什么?是加是減，是乘是除?還是其他什么?不知道問題的所在，怎樣能得出正確的答案？”

(中文來自：小故事網 翻譯:Ellison)