Late last month the world witnessed December 21, 2012, the so-called “Doomsday.” That event and another occurrence in school that made me think about how quickly time passes.

In English class my teacher, Mr. Wang, made a calculation that showed us we had only “two and a half days” to listen to his lectures before the National College Entrance Examinations.

By the calendar, it was more than 150 days before the vital exams, which start June 7 each year. But Mr. Wang reminded us that we will have at least one month off for holidays. There will be three days off because of New Year’s Day. The Spring Festival holidays will last three weeks. As for Qingming Festival, we’ll also enjoy several leisure days. And the May Day holiday will take another three days. Additionally, we will have a physical checkup prior to the entrance exams, taking up another day.

So, of the 150 days, about 120 are left. Of the 120 days, five-sevenths are school days. We have only one English class each day, meaning just 90 classes in total. Every period lasts 45 minutes, but Mr. Wang’s lecture lasts 40 minutes. That means we can listen to him for 60 hours in total. If he talked nonstop, he said, we would have only “two and a half days” to enjoy listening to him.

After the calculation, Mr. Wang wrote on the blackboard the following sentence:

“Time, though legless, runs very fast.”

The calculation shocked and awakened me. I had always thought that I had plenty of time to study. But now I come to realize that the time left is limited.

What the doomsayers said about the Mayan end-of-the-world prophecy has proven to be a fallacy. I got up that morning with a beam of sunlight penetrating the window.

I never believe the doomsayers. But I know that doomsday won’t be far away if I do nothing in my life. I realize that I should concentrate on my studies and make full use of the “two and a half days.” Time runs so fast, though it has no legs.