The ratio of speed of a motor boat in still water and that of the current of water is $25 : 4 $. The motor boat goes distance downstream in 5 hours 15 minutes. How much time will it take to come back

$t=7\frac{1}{4}hr $

The correct answer is option (4) :$t=7\frac{1}{4}hr $

Given,

Speed of motor boat in still water :Speed of current= 25 : 4

Let the speed of motor boat in still water be 25 km/h and that of speed of current be 4x km/hr.

Let the time taken by the motor boat to come back be t hrs.

then $29x×5\frac{1}{4}=21x×t$

$t= \frac{29}{4}hr$

$t=7\frac{1}{4}hr $