The speed of the river is 2 km / h. How long does it take for a boat to cover 30 km downstream

The speed of the river is 2 km / h. How long does it take for a boat to cover 30 km downstream if it covers this distance upstream in 5 hours?

1. If the movement is against the flow of the river, then the speed of the current must be subtracted from the speed of the boat V: V – 2.
2. Find out the speed of the boat.
V – 2 = 30/5;
V – 2 = 6;
V = 6 + 2;
V = 8 km / h.
3. If the movement takes place along the course of the river, then the speeds of the boat and the river are summed up: V + 2. Find out the time of movement.
t = S / (V + 2) = 30 / (8 + 2) = 30/10 = 3 hours.
Answer: in 3 hours.