The distance between the two marinas is 75 km. Moving along the river, the boat covered this distance in 2.5 hours.

The distance between the two marinas is 75 km. Moving along the river, the boat covered this distance in 2.5 hours. The speed of the boat in still water is 11 times the speed of the river. What is the speed of the boat going against the river?

Let’s find the speed of the boat along the river:
75 / 2.5 = 30 km / h;

Let’s designate: x km / h – river flow speed. This means that the boat’s own speed is 11x km / h. According to the condition of the problem, an equation was drawn up:
11x + x = 30;

12x = 30;

x = 30/12;

x = 2.5;

If x = 2.5, then 11x = 11 * 2.5 = 27.5.

Let’s find the speed of the boat against the stream of the river:
27.5 – 2.5 = 25 km / h.

Answer: the speed of the boat against the stream of the river is 25 km / h.