Ishwar is rowing a boat. He takes half time in moving a

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Ishwar is rowing a boat. He takes half time in moving a certain distance downstream than upstream. What is the ratio of the rate of boat in still water to the rate of current ?

1. 2 : 1
2. 5 : 1
3. 7 : 1
4. 3 : 1

Correct Option: D

Let speed of Ishwar's boat in still water be x km/h
and speed of current = y km/h
Rate downstream = (x + y) km/h
Rate upstream = (x - y) km/h
Let the distance covered in each case be a.
According to the question,
2a/(x + y) = a/(x - y)
⇒ 2(x - y) = x + y
2x - 2y = x + y
⇒ x = 3y
∴ x/y = 3/1
⇒ x : y = 3 : 1