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

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. Let us take x as the boat’s own speed, then the speed of the boat downstream is (x + 2) km / h, the speed against the current is (x – 2) km / h.
2. Against the current, the boat covered 30 kilometers in 5 hours. Let’s find its speed:
30/5 = 6 (km / h);
3. 6 = x – 2;
x = 6 + 2;
x = 8;
The boat’s own speed is 8 km / h.
4. Speed of the boat downstream:
8 + 2 = 10 (km / h);
5. Let’s find the time for which the boat will pass 30 kilometers downstream:
30/10 = 3 (hours);
Answer: 3 hours.