Question

At spinet torture middle school, 35% of the classrooms are for sixth graders, if there are 49 sixth grade classrooms, how many classrooms in total?

Answer 1

actually, there are a total of "x" classrooms, which oddly enough is the 100%, and we also know that 35% of that is 49, so

`\begin{array}{ccll} Amount&\%\\ \cline{1-2} x & 100\\ 49& 35 \end{array} \implies \cfrac{x}{49}~~=~~\cfrac{100}{35} \\\\\\ \cfrac{ x }{ 49 } ~~=~~ \cfrac{ 20 }{ 7 }\implies 7x=980\implies x=\cfrac{980}{7}\implies x=140`