<PRE><B>Question 727128</B>
How many liters of a 10% solution of acid should be mixed with 60% solution of acid to obtain 20 liters of 50% solution? 
----
Quantity Eq: t + s = 20 liters
Acid Eq::   10t+60s = 50*20
-------
Modify:
6t + 6s = 6*20
t  + 6s = 5*20
-----
5t = 1*20
t = 4 liters (amt. of 10% solution needed)
==============
Cheers,
Stan H.</PRE>