Answer:
The speed of the normal train is 60 kilometers per hour.
Explanation:
Let suppose that both trains move at constant speed and cover the same distance. Then, we have the following identity:
(1)
Where:
- Average speeds of the express train and the normal train, in kilometers per hour.
- Travel times of the express train and the normal train, in hours.
In addition, there is the following relationship between average speeds:
(2)
By (2) in (1), we have the following expression for the average speed of the normal train:



If we know that
and
, then the average speed of the normal train is:


The speed of the normal train is 60 kilometers per hour.