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A 400 milliliter solution is 20% alcohol by volume. If 100 milliliters of water is added, what is the new concentration

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by VJesus12 » Sat May 30, 2020 3:17 pm
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A 400-milliliter solution is 20% alcohol by volume. If 100 milliliters of water is added, what is the new concentration of alcohol, as a percent of volume?

(A) 5%
(B) 10%
(C) 12%
(D) 12.5%
(E) 16%

[spoiler]OA=E[/spoiler]

Source: Manhattan GMAT
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Junior | Next Rank: 30 Posts
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Re: A 400 milliliter solution is 20% alcohol by volume. If 100 milliliters of water is added, what is the new concentrat

by orthodoxparadox » Sat May 30, 2020 11:31 pm
Initially, the solution is \(20\%\) alcohol by volume.

This means that out of 400 ml of the solution,
Volume of alcohol = $$\frac{20}{100}\ \cdot\ 400\ =\ 80$$

Since, we add 100ml water to this solution, the volume of solution becomes 500ml, but the volume of alcohol does not change.

So, now the concentration of alcohol is \(\frac{80}{500}\ \cdot\ 100\ =\ 16\%\ \) E
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