SOLUTION :
Let the numbers are $x$ and $y$.
$\begin{array}{c}\therefore \quad x+y=11 \\x y=18\end{array}$
Dividing eqn. 1 by 2 ,
$\begin{aligned}& \frac{x+y}{x y}=\frac{11}{18} \\\therefore \quad & \frac{1}{y}+\frac{1}{x}=\frac{11}{18} ; \text { Ans. }\end{aligned}$
