The speed of a motor boat in still water is 14.4 times the speed of the current of water. If the motor boat covers a certain distance upstream in 6 hours 25 minutes, then the time taken by the motor boat to come back is :

5 hours 35 minutes

The correct answer is Option (1) → 5 hours 35 minutes

Let the speed of the current be c. Then, the speed of the water is 14.4 c.

Upstream speed = $14.4 c - c=13.4c$

Downstream speed = $14.4c+c=15.4c$

The boat covers a certain distance d upstream in 6 hour 25 min,

$d=13.4c×\left(\frac{72}{12}hr\right)$

for the downstream journey,

$T_{down}=\frac{d}{downstream\,speed}=\frac{13.4c×\frac{72}{12}}{15.4c}$

$=\frac{67}{77}×\frac{72}{12}=\frac{67}{12}hrs$

= 5 hours 35 minutes