Question 379493
Let x=amount of pure apple juice that needs to be added
Now we know that the amount of pure apple juice that exists before the mixture takes place is equal to the amount of pure apple juice that exists after the mixture takes place.
Pure apple juice before the mixture takes place:
0.20*4+x
Pure apple juice after the mixture takes place:
0.30(4+x)
Soooooo:
0.20*4+x=0.30(4+x) simplify
0.80+x=1.2+0.30x  subtract 0.30x and also 0.80 from each side
x-0.30x=1.2-0.80 
0.70x=0.40
x=4/7 =0.57 gal--amount of pure apple juice needed
CK
0.20*4+0.57=0.30(4.57)
0.80+0.57=1.371
1.37~~~1.371

Hope this helps---ptaylor