Speed of a boat in still water is 10 km/hr. It takes total 20 hrs to cover a distance of 91 km in upstream and 91 km in downstream. Find speed of current.

03 km/hr

Let speed of current = v km/hr

Speed of boat in downstream = (10 + v) km/hr

Speed of boat in upstream = (10 - v) km/hr

ATQ,

\(\frac{91}{10\;+\;v}\) - \(\frac{91}{10\;-\;v}\) = 20

Now, check from option, nearest value which can divide 91 easily when adding and subtracting with 10.

Hence, 3 is the option which satisfy the equation.