So if you took 4 hours to travel 200 kilometers, you would have traveled at a speed of 50 km/h.
But it is important to realize that if you are given details of two separate legs of a journey, you cannot just average the given speeds to find the average speed. For example, if a family travel from Portsmouth to Brighton at a speed of 70 km/h and return from Brighton to Portsmouth at a speed of 40 km/h, the average speed is most certainly not
half of (70+40) = 55 km/h
Many problems at GCSE deal with idealized situations where people travel for long distances at constant speed.
If we were to describe a journey by plotting it on a distance-time graph