The boat covered the distance between the piers along the river in 2 hours, and the return trip took 2.5 hours

The boat covered the distance between the piers along the river in 2 hours, and the return trip took 2.5 hours. The current speed is 2 km / h. Find the distance between the marinas.

The solution of the problem:

Let the distance between the marinas be x.

Then the speed of the boat along the river is x / 2.

And the speed of the boat against the stream of the river is x / 2.5.

The speed of the river flow is equal to half the difference between the speed of the boat along the river and the speed of the boat against the current of the river, we get the equation:

(x / 2 – x / 2.5) / 2 = 2;

2.5x / 5 – 2x / 5 = 2 * 2 = 4;

0.5x / 5 = 4;

0.5x = 20;

x = 40 (km) – distance between quays.

Answer: The distance between the marinas is 40 km.