The speed of a motor boat is that of the current of water as 36:5. The boat goes along with the current in 5 hours 10 min, it will come back in_______?

A. 5 hours 50 min
B. 6 hours
C. 6 hours 50 min
D. 12 hours 10 min
Explanation:
Let the speed of motor boat be 36x km/hr and that of current of water be 5x km/hr
Speed downstream = (36x +5x)km/hr = 41x km/hr
Speed upstream = (36 -5x)km/hr = 31x km/hr
Distance covered downstream = (41x × 31/6)km
Distance upstream = [1271x/6 × 1/31x]hrs
= 41/6 hrs = 6hrs 50 min