A boatman goes 6 km upstream and return to the starting point in 2 hrs. If the speed of current is 4 km/hr, then find the speed of boat in still water.
Answer & explanation
Correct answer: option 2
Let the speed of boat in still water =u km/hr
and the speed of current = v km/hr = 4 km/hr
Speed of boat in downstream = u + v
Speed of boat in upstream = u - v
Now ATQ,
\(\frac{6}{u + v}\) + \(\frac{6}{u - v}\) = 2 hrs
\(\frac{6}{u + 4}\) + \(\frac{6}{u - 4}\) = 2 hrs
Checking options, u = 8 satisfies the above eq.
Speed of boat in still water = 8 km/hr