Suppose that a person rows a boat in still water at the speed of 10 km/hr and the water runs at the speed of 4 km/hr. This person travels a certain distance & then returns. If it takes 4 hrs more for him to travel upstream than that of downstream then what will be the distance?
30 km
40 km
42 km
32 km
Explanation:
Distance =$\dfrac{t\left(x^2-y^2\right)}{2y}km$
Given parameters are:
Speed of a boat in still water x= 10 km/hr
Speed of running water y= 4 km/hr
Required time t= 4 hrs to travel upstream more than downstream
Therefore, we obtain,
Distance =$\dfrac{t\left(x^2-y^2\right)}{2y}$
=$\dfrac{4\left(10^2-4^2\right)}{2\times4}$
= 42 km