A certain distance is covered at a certain speed.If half of this distance is covered in double the time, the ratio of two speeds is
Distance = Rate * Time
The problem statement asks about the ratio of speeds, so it may be prudent to solve for speed.
Rate1 = Distance / Time
"If half of this distance is covered in double the time"
Rate2 = (Distance/2) / (2*Time) = (Distance / Time)/4