Question 1054919
let x = the number of liters of the 20% solution.


let y = the number of liters of the 60% solution.


you want x + y to be equal to 40 liters.


x is the number of liters total in the first solution.
y is the number of liters total in the second solution.


you want .2 * x + .6 * y to be equal to .35 * 40


.2 * x is the number of liters of acid in the first solution.
.6 * y is the number of liters of acid in the second solution.
.35 * 40 is the number of liters of acid in the final solution.


you have two equations that need to be solved simultaneously.


they are:


x + y = 40
.2x + .6y = .35*40


simplify these equations to get:


x + y = 40
.2x + .6y = 14


you can solve by substitution or by elimination or by graphing.
i will solve this one by graphing.
this means to graph both equations and find the intersection.


the graph looks like this:


<img src = "http://theo.x10hosting.com/2016/102903.jpg" alt="$$$"


the graph says the intersection is at the coordinate point of (25,15).


this means that x = 25 and y = 15.


x is the number of liters of the 20% solution.
y is the number of liters of the 60% solution.


the formula of .2x + .6y = 14 becomes .2 * 25 + .6 * 15 = 14.
simplify this equation to get 14 = 14.
this confirms the solution is good.