Question 88945
Let x=syrup concentration in the remaining mixture that must be added which is 12-8 or 4 oz

Now we know that the amount of pure syrup in the 8oz mixture (0.30(8)) plus the amount of pure syrup in the 4oz mixture (x(4)) must equal the amount of pure syrup in the final mixture (0.42(12)).

So our equation to solve is:

0.30*8+4x=0.42*12
2.40+4x=5.04  subtract 2.40 from both sides

2.40-2.40+4x=5.04-2.40  collect like terms

4x=2.64  divide both sides by 4

x=0.66--or 66%--------syrup concentration in the remaining mixture that must be added 

CK

0.30*8+0.66*4=0.42*12

2.40+2.64=5.04
5.04=5.04

Hope this helps---ptaylor