A boat covers a certain distance downstream in 4 hours, but takes 6 hours to return to the starting point. What is the ratio of speed of stream to the speed of the boat in still water?

Correct option is D

Let the speed of boat be x;
The speed of stream be y
Distance covered in down stream will be = (x+y)×4
Time taken in upstream is = 6 hours
Since distance covered in both side will be same so we have
(x+y)×4 =(x-y)×6
4x +4y =6x-6y
10y =2x
y/x=1/5
x/y =5/1

Ratio of speed of strem and speed of boat = 1 : 5