Use a system of equations to solve this problem. dr. graham currently has two acid solutions. she only has a 60% acid solution and a 20% acid solution in her lab. dr. graham needs 30 l of a 50% acid solution to conduct an experiment. how many liters of each solution should she mix together? let x = the amount of 60% acid solution

Dr. Graham currently has two acid solutions.
60% acid AND 20% acid
Dr. Graham needs 30 L of a 50% acid solution
We set up 2 equations in which s = 60% acid and t = 20% acid
A) s + t = 30
B) .60s + .20t = (.50 * 30)
We multiply equation A by -.20
A) = -.20s -.20t = -6 then we add it to B)
B) .60s + .20t = 15
.40s = 9
s = 22.5
t = 7.5
So, she needs to mix 22.5 liters of 60% acid with 7.5 liters of 20% acid.

Source:
http://1728.org/mixture.htm