Correct Answer - Option 3 : 5 km/h
Given:
The speed of a boat in still water = 25 km/h
It covers a distance of 105 km in 5 hours 15 minutes in upstream direction.
Concept:
If the speed of a boat in still water = x km/h and
the speed of current = y km/h than,
Speed of a boat in the same direction of current (downstream) = (x + y) km/h
Speed of a boat in the opposite direction of current (upstream) = (x - y) km/h
Calculation:
x = 25 km/h
5 hours 15 minutes = 21/4 hours
x - y = 105/(21/4) = 20 km/h
⇒ 25 - y = 20
⇒ y = 5 km/h
∴ The speed of stream is 5 km/h.
