A man can row a boat at 8 km/h in still water. If the speed of the water current is 2 km/h and it takes him 2 hours to row to a place and come back, then how far off (in km) is the place?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 7.5
Speed of the boat = 8km/h
Speed of the current = 2km/h
Downstream speed = Speed of the boat + Speed of the current = 8 + 2 = 10 km/h
Time = \(\frac{Distance}{Speed}\)
Upstream speed = Speed of the boat - Speed of the current = 8 - 2 = 6km/h
According to the question,
\(\frac{D}{10}\) + \(\frac{D}{6}\) = 2
\(\frac{3D + 5D}{30}\) = 2
8D = 60
D = 7.5 km