sum means add
the number is x
13 divided by a number is 13/x
the number divided by the number is x/13
so
[tex]\frac{13}{x}+\frac{x}{13}[/tex]
also can be simplified to
[tex]\frac{169}{13x}+\frac{x^2}{13x}[/tex] or
[tex]\frac{x62+169}{13x}[/tex]
translated it is [tex]\frac{13}{x}+\frac{x}{13}[/tex] where x is the number
