Question 23079
Follow the acid.
Start with 20%x acid
Add 80%(200-x) acid
End up with 50%(200)acid
EQUATION:
20x +80(200-x) = 50(200)
20x +16000 - 80x = 10000
            -60x = -6000
x = 100 liters of 20% solution
200-x= 100 liters of 80% solution

Cheers,
Stan H.