SOLUTION: rubbing alcohol is typically diluted with water to 70% strength. if you need 2.8 oz of 45% rubbing alcohol, how many ounces of 70% rubbing alcohol and how much water should you com

Question 941109: rubbing alcohol is typically diluted with water to 70% strength. if you need 2.8 oz of 45% rubbing alcohol, how many ounces of 70% rubbing alcohol and how much water should you combine. I know the formula is a.c = q but when sitting up the equation i am very confused. Please help! Thank you in advance.
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39618) (Show Source): You can put this solution on YOUR website!
The water itself as a separate material is 0% alcohol.

Mixing two concentrations for known amount of mixture
http://www.algebra.com/my/Mixtures%3A-All-in-Symbols.lesson?content_action=show_dev
Answer by MathTherapy(10552) (Show Source): You can put this solution on YOUR website!
rubbing alcohol is typically diluted with water to 70% strength. if you need 2.8 oz of 45% rubbing alcohol, how many ounces of 70% rubbing alcohol and how much water should you combine. I know the formula is a.c = q but when sitting up the equation i am very confused. Please help! Thank you in advance.

Water + water = water
Let amount of water to mix, be W
The 70% alcohol mixture contains 70% alcohol and 30% water
Amount of mixture before water is added: 2.8 - W
The resulting 45% alcohol mixture will contain 45% alcohol and 55% water
Therefore, we get: .3(2.8 - W) + W = .55(2.8)
.84 - .3W + W = 1.54
- .3W + W = 1.54 - .84
.7W = .7
W, or amount of water to add = , or oz
You should be able to calculate the amount of alcohol in the mixture.
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