If x : y = 4 : 15 then the value of $$\left( {\frac{{x - y}}{{x + y}}} \right)$$   is?

$$\eqalign{ & y:x = 4:15 \cr & \therefore \frac{y}{x} = \frac{4}{{15}} \cr & \therefore \frac{{x - y}}{{x + y}} \cr & \Rightarrow \frac{{x\left( {1 - \frac{y}{x}} \right)}}{{x\left( {1 + \frac{y}{x}} \right)}} \cr & {\text{Taking }}x{\text{ common}} \cr & \Rightarrow \frac{{1 - \frac{4}{{15}}}}{{1 + \frac{4}{{15}}}} \cr & \Rightarrow \frac{{11}}{{15}} \times \frac{{15}}{{19}} \cr & \Rightarrow \frac{{11}}{{19}} \cr} $$