Correct Answer - Option 3 : 14
Given:
A boat travels a certain distance upstream in 7 hours when speed of stream is 4 km/hour. It takes 2 hours to travel 20 km downstream.
Formula used:
Upstream = (u−v) km/hr
Downstream = (u+v) Km/hr
Where “u” is the speed of the boat in still water and “v” is the speed of the stream
Speed of Boat in Still Water = 1/2 (Downstream Speed + Upstream Speed)
Speed of Stream = 1/2 (Downstream Speed – Upstream Speed)
Calculation:
Let the speed of the boat in still water be x and the distance be d.
d = 7 × (x - 4)
20 = 2 × (x + 4)
⇒ x = 6
⇒ d = 7 × (x - 4) = 7 × (6 - 4) = 14
∴ The distance it covered upstream is 14 km.
