DRDO Multi tasking staff Model paper 8

Speed of boat in still water = B = 3 km/hr
Speed of stream = S = 1 km/hr
Speed of boat going downstream = B + S = 3 + 1 = 4 km/hr
Speed of boat going upstream = B - S = 3 - 1 = 2 km/hr
Let the distance of the place be d.
Time taken to go to that place = Distance/Speed of boat downstream = d/4 hr
Time taken to come back from that place = Distance/Speed of boat upstream = d/2 hr
Total time taken to go and come back to that place = 9 hr
⇒ d/4 + d/2 = 9
⇒ 3d/4 = 9
⇒ d = 12 km