A boat travels 68 km. downstream and 45 km. upstream in 9 hrs. If boat travels 51 km. downstream and 72 km. upstream in 2 hrs more, then find speed of stream and speed of boat in still water.

4 km/hr, 13 km/hr

Let the speed of boat = U km/hr.

Speed of stream = V km/hr.

ATQ,    \(\frac{68}{U+V}\) + \(\frac{45}{U - V}\) = 9   -----------(i)

            \(\frac{51}{U+V}\) + \(\frac{72}{U-V}\) = 11 ----------- (ii)

Note : - Take help of common factor for speedy calculations

                    (68, 55)  and   (45, 72)

                      ⇓    ⇓                ⇓    ⇓

                         17                   9

So, U+V = 17 and U-V = 9 satisfy the equation

Then, U = 13 km/hr and V = 4 km/hr