Correct Answer - Option 2 : 11
Given:
A boat travels a certain distance downstream in 8 hours when speed of stream is 7 km/hour. It travels 6 km more upstream in 37.5 hours.
Formula:
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 = 8 (x + 7)
⇒ D + 6 = 37.5 (x - 7)
⇒ 8(x + 7) + 6 = 37.5 (x - 7)
⇒ x = 11
∴ Speed of the boat in still water = 11 km/hour