At first glance it may seem that a horrendous calculation is necessary to solve this: the sum of an infinite series of numbers that get smaller and smaller as the cars approach each other. But if you focus on time rather than distance, a solution is easy. The cars are 50 miles apart and traveling towards each other at a combined speed of 50 miles per hour, so they will meet in one hour. In that hour, a fly that flies at 100 miles per hour will naturally travel 100 miles.