# Math Help - Help me Fast for a College Class!!!

1. ## Help me Fast for a College Class!!!

Question is: How many gallons of a solution of glycerine and water containing 55% glycerine should be added to 15 gallons of a 20% solution to give a 40% solution??

2. Originally Posted by Brooke
Question is: How many gallons of a solution of glycerine and water containing 55% glycerine should be added to 15 gallons of a 20% solution to give a 40% solution??
Begin, to knowing that,
$\mbox{concetration }=\frac{\mbox{volume of substance}}{\mbox{total volume}}$

Solution 1 has 55% of x gallons is glycerine which is $.55x$ gallons.
Solution 2 has 20% of 15 gallons is glycerine which is $.2\cdot 15=3$ gallons.
Thus when you combine them,
you have $.55x+3$ is amount of glycerine.
and, in total you have,
$x+15$
And you want 40% thus,
$\frac{.55x+3}{x+15}=.4$
Thus,
$.55x+3=.4(x+15)$
Thus,
$.55x+3=.4x+6$
Thus,
$.15x=3$
Thus,
$x=20\mbox{ gallons}$