A man rows to a place 35 km in distance and back in 10 hours 30 minutes. He found that he can row 5 km with the stream in the same time as he can row 4 km against the stream. Find the rate of flow of the stream.

0.75 km/hr

If time is same, then ratio of distance = ratio of speed

                       (D.S) Downstream :   (U.S) upstream

            Distance                5R       :           4R

            Speed                   5R       :           4R

ATQ,       \(\frac{35}{5R}\) + \(\frac{35}{4R}\) = 10\(\frac{1}{2}\) hrs

              \(\frac{35 × 9R}{20 R^2}\) =  \(\frac{21}{2}\)  

                                                      R = 1.5

              Speed of stream = \(\frac{5R - 4R}{2}\) × 1.5 = 0.75 km/hr