If the ratio of speed of upstream and down stream is  $3:4$, then the ratio of the speed of boat in still water and the speed of the stream is

Let speed of boat in still water be $\text{'}x\text{'}kmph$

$\therefore$ let speed of stream be $\text{'}y\text{'}kmph$

Speed of boat up stream $=(x-y)kmph$

Speed of boat down stream $=(x+y)kmph$

Given ratio of speed of boat up stream and down stream$=3:4$

$\therefore$$\frac{x-y}{x+y}=\frac{3}{4}$

$4(x-y)=3(x+y)$

$4x-4y=3x+3y$

$4x-3x=3y+4y$

$1x=7y$

$\frac{x}{y}=\frac{7}{1}$

$\therefore$ $x:y=7:1$

Ratio of speed of boat in still water and speed of the stream  $=7:1$