<PRE><B>Question 1025825</B>
I prefer to teach this with the single variable method.

X is the amount of pure acid needed
126-X is the 10% solution needed.

You see, this eliminates the need for 2 variables, since we know they add to 126, both amounts are expressed in terms of each other.

100X+10(126-X)=20(126)

100X+1260-10X=2520

90X=1260

X=14

14 liters pure acid
112 liters 10% acid containing 11.2 liter acid.

total 25.2liters of acid in 126 liters solution is 25.2/126 = 20%</PRE>