now, let's say there are "b" boys and "g" gals... ok... well, we know there are 116 more boys than gals..... so, if there are "g" gals then there must be "g + 116" boys.
[tex]\bf \cfrac{boys}{girls}\qquad 9:7\qquad \cfrac{9}{7}\implies \cfrac{9}{7}=\cfrac{\stackrel{boys}{g+116}}{\stackrel{girls}{g}}\implies 9g=7g+812
\\\\\\
2g=812\implies g=\cfrac{812}{2}\implies g=\stackrel{girls}{406}[/tex]
what's the total class? well is g + b or g + ( g + 116).
