500 個 螞蟻隨機放在一米的線上（單一分配Uniform distribution) . 每一個螞蟻會隨機在向兩邊的線頭，以均速每分鐘1米走，等到離開線頭。 但當遇到另一個螞蟻的時候， 他們會掉頭走（反方向），再以均速每分鐘1米走。

假設螞蟻是無限小。 


請問預計所有螞蟻離開的時間 （平均時間expected time ）

you are so fast. Please explain the reason

You are all in right direction. Perhaps you guys can make the answer...I don't need to post

haha..Too many smart people here. Perhaps I should put more challenging question next time.