<PRE><B>Question 177629</B>
let x be the amount of pure alcohol added
:
existing solution+added solution=final mixture
:
.10(7)=existing
:
x = pure alcohol added
:
.3(7+x)=final mixture(see we want to end up with 30% of what we are mixing and thats the original 7 liters plus what ever we add.
:
so putting it altogether we have
:
.10(7)+x=.3(7+x).....eq 1
:
.7+x=2.1+.3x
:
.7x=1.4
:
{{{highlight(x=2)}}}Liters of pure alcohol</PRE>