Question 815264
"How many liters of a 10% solution of acid should mixed with 60% solution of acid to obtain a 20 liters of 50% solution?"

Do I need to use 2 variables? And will my set up of the equation be 
"x(.10)+y(.60)=20(.50)" ? or are there errors that must be corrected?
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x(.10)+y(.60)=20(.50)
That's one equation, for the amount of acid.
x + y = 20 is the other.