The boat’s own speed is 13 km / h, the speed of the river is 3 km / h. The distance between the two berths is 80 km.

The boat’s own speed is 13 km / h, the speed of the river is 3 km / h. The distance between the two berths is 80 km. How long will the boat cover this distance if it is sailing: along the river, against the river.

By the condition of the problem, the distance S between two berths:

S = 80 km.

If the boat will sail along the river, then its speed is V:

V = 13 km / h + 3 km / h = 16 km / h.

The boat will sail with the flow for time T:

T = S / V = 80/16 = 5 hours.

If the boat will sail against the current of the river, then its speed is V:

V = 13 km / h – 3 km / h = 10 km / h.

The boat will sail against the current for time T:

T = S / V = 80/10 = 8 hours.