so, if we take 800 as the 100%, the increase is 900-800 or 100, what is 100 in percentage of 800?
well [tex]\bf \begin{array}{ccllll}
amount&\%\\
\textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\
800&100\\
100&x
\end{array}\implies \cfrac{800}{100}=\cfrac{100}{x}[/tex]
solve for "x"
