From two cities, the distance between which is 45 km, trains with speeds of 70 km / h and 60 km / h

From two cities, the distance between which is 45 km, trains with speeds of 70 km / h and 60 km / h simultaneously left in one direction, and the first train is catching up with the second. How long will the distance between trains be 10 km? How many solutions does the problem have?

Let’s find the speed at which the first one is catching up with the other:

70 – 60 = 10 km / h.

At the time when the distance between them is 10 km, the trains will approach each other by:

45 – 10 = 35 km.

Then it will happen through:

35:10 = 3.5 hours.

Answer: the required time is 3.5 hours.