小明又来找Z老师谈解题心得.题目是这样的:每小时一架飞机从达尼丁飞往上海,同时每小时另一架飞机从上海飞往达尼丁,一次飞行需10小时完成.一名旅客从达尼丁到上海的一次旅行中遇上反方向飞来的飞机的架数是(包括所乘飞机起飞或降落时见到的正好降落或起飞的另一架飞机).小明说 Xiaoming came to Z to talk about the problem. The topic was this: An airplane flying from Dunedin to Shanghai every hour, and another plane per hour from Shanghai to Dunedin, a flight takes 10 hours to complete The number of planes that a passenger flew in the opposite direction from a trip to Dunedin to Shanghai was (including another airplane that just landed or took off when he was taking off or landing). Say