Correct Answer - Option 1 : 25 km/h
Given:
Distance travelled upstream = 80 km
Time taken upstream = 4 hrs
Distance travelled downstream = 60 km
Time taken downstream = 2 hrs
Concept:
Upstream speed means the boat is going against the stream and its speed is reduced due to the flow of water against the boat. Downstream speed means the boat is flowing with the water, so its speed increases.
Formula used:
Speed of boat in still water = (Downstream speed + Upstream speed)/2
Calculation:
Downstream speed of the boat = (60/2) km/h
= 30 km/h
Upstream speed of the boat = (80/4) km/h
= 20 km/h
∴ Speed of boat in still water = (30 + 20)/2 km/h
= (50/2) km/h
= 25 km/h
