SOLUTION: How much water should be added to 20 ounces of a 15% solution of alcohol to dilute it to a 10% solution?

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Question 10331: How much water should be added to 20 ounces of a 15% solution of alcohol to dilute it to a 10% solution?
Answer by Earlsdon(6103) About Me  (Show Source):
You can put this solution on YOUR website!
Here's one approach.
20 ounces (oz) of a 15% alcohol solution has 85% water.
The 10% alcohol solution has 90% water. You need to add x ounces (oz) of 100% water.
Change percents to decimals.
20 oz(.85) + x oz(1.0) = (20+x)oz(0.9) Simplify and solve for x.
17 + x = 18 + 0.9x Subtract 0.9x from both sides.
17 + 0.1x = 18 Subtract 17 from both sides.
0.1x = 1 Divide both sides by 0.1
x = 10
Add 10 oz of water.