Didn't that question name a starting point like X and a turn-around point like Y, so that the distance was fixed?
Yrs the distance is fixed, but the question didn't say what the distance from point x to point y was. That's where I got stuck. I just thought too much about it. After playing with different numbers, I now know why the 20/20 racer wins.
The 30/10 racer goes 1.5 times faster on the way out, but the 20/20 racer comes back at 2 times his rate. He can never make that time up.