The boat passed 40 km along the lake in 2 hours and 34 km along the river for another 2 hours.

The boat passed 40 km along the lake in 2 hours and 34 km along the river for another 2 hours. Determine the speed of the river.

A lake differs from a river in that the river has a certain flow rate.

If the boat traveled a shorter distance along the river than in still water – in a lake, it means that it was moving along the river against the current.

We will use the formula:

v = S / t, where v is speed, S is distance and t is time.

Let’s determine the speed of the boat in the lake:

40/2 = 20 km / h.

Let’s determine the speed of the boat in the river:

34/2 = 17 km / h.

The speed of the river flow is the difference between the speed of the boat in still water and the speed of the boat against the current of the river, that is:

20 – 17 = 3 km / h.