An express train travel from A to B for 4 hours. A normal train travel from B to A for 10 hours. Both of them started at the same time. The average speed of the express train is greater than the average speed of the normal train 90km/h. Find the average speed of the normal train?

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

Step-by-step 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.

b

step-by-step explanation: