SOLUTION: rosa combines 2 gallons of 2% milk and 6 gallons of 4% milk. How many gallons of 6% milk must she add to obtain a 5% milk mixture?

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Question 951413: rosa combines 2 gallons of 2% milk and 6 gallons of 4% milk. How many gallons of 6% milk must she add to obtain a 5% milk mixture?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
First mixture, %282%2A2%2B6%2A4%29%2F%282%2B6%29=28%2F8, percent. Eight gallons of this.

Use that number unreduced here:

Next mixture, %28%2828%2F8%29%2A8%2Bv%2A6%29%2F%28v%2B8%29=5, using v for how much of the 6% fat milk to add.

28%2B6v=5%28v%2B8%29
28%2B6v=5v%2B40
v=40-28
highlight%28v=12%29 gallons of the 6% to add.