Correct Answer - Option 3 : 38.4 hrs
Given:
Ship covered 96 km upstream = 32 hours
Speed of current = 1 / 4th of speed of ship
Formula:
Speed = Distance / Time
If speed of motor boat and stream be x and y km / hr respectively, then
Upstream speed = (x - y) km / hr
Downstream speed = (x + y) km / hr
Calculation:
Let speed of ship in still water be 4x km / hr
Speed of current = 4x × (1 / 4) = x km / hr
According to the question
Upstream speed = 4x – x = 3x
According to the question
3x = 96 / 32
⇒ x = 3 / 3
⇒ x = 1
Downstream speed = 4x + x = 5x = 5 × 1 = 5 km / hr
Double the distance of 96 km = 2 × 96 = 192 km
∴ Time taken by ship to cover 192 km along the current = 192 / 5 = 38.4 hrs