SSC MTS 2022 PYQ — Question 60

The correct answer is option 1 i.e. 6 hours

Let the speed of the motor-boat be x km/h and the speed of the current be y km/h.

Now,

Ratio of speed of the motor-boat  to the speed of the current of the water = 20 : 4

⇒ x : y = 20 : 4

⇒ x = (20y/4) = 5y

Speed along the current of the water = x + y 

Speed against the current of the water = x - y

Distance covered = Speed x time taken

Distance covered = $(x+y)\times4$

Also,

Distance covered = $(x-y)\times t$

On equating both,

$(x+y)\times4 = (x-y)\times t$

⇒ $(5y+y)\times4 = (5y-y)\times t$

⇒ $t=6$

Hence,

The time taken by the boat to cover the same distance against the current is 6 hours.