Liuka, a famous French mathematician. At an international scientific conference in the18th century, at breakfast one day, Liuka raised the following question and said it was the "most difficult" problem here. The topic is: Suppose a shipping company has a ship from new york to Harvard at noon every day, and a ship from Harvard to new york at the same time every day. The time of the ship on the way is 7 days and nights, all of which are driving on the same route at a constant speed, and the ships coming and going can see each other at close range. On the way to new york, how many ships of the same company can you meet from the opposite side of the ship that left Harvard at noon today? This question aroused the interest of mathematicians attending the meeting, and they answered them one after another, and got three answers: 7 ships, 14 ships, 15 ships. Which of the above three answers is correct? We can think of it this way: ships sailing from Harvard today will encounter two kinds of ships on the way: one is a ship sailing from new york seven days ago, and the other is a ship sailing from new york seven days later, that is, a ship sailing from new york 0/4 days ago. Since 14 is counted from noon on 1 day, the first seven days are noon on the eighth day and the last seven days are noon on 15, so there are 15 "noon" in * *. Therefore, according to one ship leaving at noon every day, ships leaving Harvard will meet 15 ships leaving new york. Obviously, the above answer 15 is correct.