Correct Answer - Option 4 : 3 : 1
Given:
Time is taken in downstream = half of time taken in upstream.
Concept used:
Speed ∝ 1/Time
That means reversing the ratio of time gives the ratio of speed.
Calculation:
Let the speed of the boat in still water is x km/h
And the speed of the stream is y km/h.
⇒ Downstream = (x + y) km/h
⇒ Upstream = (x - y) km/h
Ratio of time downstream : upstream = 1 : 2
Ratio of speed downstream : upstream = 2 : 1
⇒ (x + y) : (x - y) = 2 : 1
⇒ x + y = 2x - 2y
⇒ x = 3y
⇒ x/y = 3/1
Speed of the boat in still water : Speed of stream = 3 : 1
∴ Ratio of the speed in still water to the speed of current is 3 : 1
