A person can row a distance of 4 km upstream in one hour 20 minutes and can row back to the starting point in just 24 minutes. How much time (in hours) will he take to row 13 km in still water?

2

ATQ,  (U.S) Upstream speed = \(\frac{4}{1\frac{1}{3}}\) = \(\frac{4}{\frac{4}{3}}\) = 3 km/hr

        (D.S) Downstream speed = \(\frac{4}{\frac{24}{60}}\) = 10 km/hr

        Speed of boat = \(\frac{D.S + U.S}{2}\) = \(\frac{10+3}{2}\) =\(\frac{13}{2}\) km/hr

        Time taken to cover 13 km = 13 × \(\frac{2}{13}\) = 2 hr.