Question

A river is running at 2 km/hr. It took a man twice as long to row up as to row down the river. The rate (in km/hr) of the man in still water is 

(a) 8 

(b) 10 

(c) 4 

(d) 6

Answer 1

(d) 6 km/hr

Let the distance travelled be D km and speed of the man in still water be x km/hr. Then, 

Speed downstream = (x + 2) km/hr 

Speed upstream = (x – 2) km/hr 

Given, \(\frac{D}{x-2}=2\times\frac{D}{x+2}\)

⇒ \(x\) + 2 = 2\(x\) – 4 ⇒ \(x\) = 6 km/hr.