A mixture contains forty ounces of glycol and water and is ten percent glycol. If the mixture is to be strengthened to twenty-five percent, how much glycol is to be added?
4 oz
8 oz
10 oz

Question

A mixture contains forty ounces of glycol and water and is ten percent glycol. If the mixture is to be strengthened to twenty-five percent, how much glycol is to be added?
4 oz
8 oz
10 oz

hero · Answer

40 + x = y
40(.10) + x = .25y

hero · Answer

Systems of equations
Solve for x

hero · Answer

Put equations above in a form to be solved by elimination method
4 + x = .25y
-40 - x = -y

Add Fractions: 
-36 = -.75y

Divide both sides by -1: 
36 = .75y

Divide both sides by .75:

y = 48
x = 8

So 8 oz. 

But you should actually try solving these yourself rather than looking for answers.