Question 931542
No indication if this problem is about profit or revenue or price.  The concentration could be in DOLLARS PER LITER.  You can solve this as a simple two-part mixture problem.


Let x for how much water, 0 dollars per gallon



{{{(10*10+20*30)/(10+20)=priceOfOriginalMixture}}}
{{{600/30=60/3}}}
{{{highlight(20)}}} dollars per liter, the original mixture.  There are 30 liters of this original mix.


HOW MUCH WATER to make mixture concentration of 1$ per liter?
{{{highlight((30*20+x*0)/(30+x)=1)}}}.
MOST important is to understand this equation and the one which lead up to it.  Once understood, roll this the rest of the way yourself.