Question 186933
Ok, YOU DO THE TABLE AND I WILL SET UP THE EQUATION :

Let x= amount of wine needed
Then 20-x=amount of peach schnapps needed

Amount of pure alcohol before the mixture = amount of pure alcohol after they are mixed, so:
0.25x + 0.50(20-x)=0.40*20 get rid of parens
0.25x+10-0.50x=8 subtract 10 from each side
0.25x+10-10-0.50x=8-10 collect like terms
-0.25x=-2  divide each side by -0.25
x=8 liters-----------amount of wine needed

CK
8*0.25+0.50*12=0.40*20
2+6=8
8=8

Now you could solve  this problem using two unknowns:
Let x=amount of wine
y=amount of schnapps
x+y=20------------------------eq1
0.25x+0.50y=0.40*20 or
0.25x+0.50y=8--------------------eq2

Hope this helps----ptaylor