Let's reverse the situation, shall we? Two cyclists start at the midpoint of a road 20 km long (yes, I know the original was in miles, it's just that I was born after the decline and fall of the Roman empire). The first starts cycling north at 10 kmh, the other south at the same speed. At the same instant, a fly starts flying between them at 20 kmh, flipping round and flying back to the other whenever it reaches one of them.
(ATTN math geeks! If this bothers you, assume the fly starts flying at some small time δ>0 after the cyclists do, and ask yourself the same question when δ-->0)
After exactly 1 hour, the cyclists reach the end of the road. QUESTION: Where is the fly at this time?
Answer to be provided here next week (or earlier if enough people beg).