A man rows to a place 48 km distant and comes back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The speed of the stream is:
Answer & explanation
Correct answer: option 4
According to the question,
Let the speed of the boat in still water be x km/h
Let the speed of the stream be y km/h
Speed of boat in up stream = (x - y) km/h
Speed of boat in down stream = (x + y) km/h
According to question;
Time = distance/Speed
= 4/(x−y) = 3/(x+y)
= 4x - 4y = 3x - 3y
= x = 7y -------(a)
Now;
48/(x+y) + 48/(x−y) = 14
= 48/(7y+y) + 48/(7y−y) = 14 -------- (from eq. (a))
= 6y + 8y = 14
= 14y = 14
The speed of the stream = y = 1 km/h