Length of river is 40 km. Speed of stream is 3 km/hr. Boat takes 6 hours more to return than to go in river. Find the speed of boat in still water.
Answer & explanation
Correct answer: option 2
Let speed of boat in still water = u km/hr
Speed of boat in downstream = (u + 3) km/hr
Speed of boat in upstream = (u - 3) km/hr
ATQ,
\(\frac{40}{u\;-\;3}\) - \(\frac{40}{u\;+\;3}\) = 6
Now, check from option, nearest value which can divide 40 easily when adding and subtracting with 3.
Hence, 7 is the option which satisfy the equation.