A boat travels 14 km. downstream and immediately returns and takes thrice time in returning. If boat speed is twice, then boat takes 336 min. in going downstream and upstream. Find speed of boat in still water.

2\(\frac{2}{3}\)

Condition (i) Let boat speed = x and stream speed = y

 \(\frac{\frac{14}{× + y}}{\frac{14}{x - y}}\) = \(\frac{1}{3}\)

\(\frac{x -y}{x + y}\) = \(\frac{1}{3}\)

        x : y = 2 : 1

Condition (ii) → \(\frac{14}{4R+R}\) + \(\frac{14}{4R - R}\) = \(\frac{336}{60}\)

\(\frac{14}{5R}\) + \(\frac{14}{3R}\) = \(\frac{28}{5}\)

\(\frac{1}{5R}\) + \(\frac{1}{3R}\) = \(\frac{2}{5}\)

                                                    R = \(\frac{4}{3}\)

Then, speed of boat = 2 × \(\frac{4}{3}\) = 2\(\frac{2}{3}\) km/hr