Question

X, Y , Z are three towns on a lake which flows uniformly. Y is equidistant from X and Z. A man rows from X to Y and returns in 20hrs. He can row from X to Z in 8 hr. The ratio of speed of the man in still water to the speed of the current is. A) 3:5 B) 5:3 C) 2:3 D) None of these

Answer 1

ANSWER: A

Explanation:

Let the speed of man in still water = x km/hr

Speed of the current = y km/hr

Speed of downstream = (x+ y) km/hr

Speed of upstream = ( x – y) km/hr

Let the lake be flowing from X to Z and

 xy = yz a

 then xz =2a.

 a / (x + y )+ a / (x – y) = 20 -----1

 and 2a / x + y = 8 ----2

 a / x + y = 4 -------3

 substitute 3 in 1

 4 + a / x – y = 20

 a / x – y = 16 ----------4

 dividing 3 and 4 we get,

 a / (x +y) * (x –y) / a = 4 / 16

 x – y / x + y = 1 / 4

 4x – 4y = x + y

 3x = 5y

x / y = 3 / 5  x : y = 3 : 5