[tex]n+50\%n=n+0.5n=1.5n\\\\1.5n\in (10,20)\ \ \ \Leftrightarrow\ \ \ 20>1.5n>10\ /\cdot2\ \ \ \Leftrightarrow\ \ \ 40>3n>20\ /:3\\\\\frac{40}{3} >n>\frac{20}{3} \ \ \ \Leftrightarrow\ \ \ 13\frac{1}{3} >n>6\frac{2}{3} \ \ \ and\ \ \ n\in I\\\\Ans.\ n\in\{7,8,9,10,11,12,13\}[/tex]
