Question

Speed of the boat in still water is 6 km/hr. The time required to go downstream in half of the time required to go upstream. Find the speed of the water current. 

(1) 5 km/hr 

(2) 4 km/hr 

(3) 3 km/hr 

(4) 2 km/hr

Answer 1

 (4) 2 km/hr 

Assume speed of stream = xkm/hr

 Downstream time\(=\frac{d}{x+6}\)

Upstream time\(=\frac{d}{6-x}\)

\(\frac{2d}{x+6}= \frac{d}{6-x} \implies 6=3x\) 

x = 2