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If a portion of a half water/half alcohol mix is replaced with 25% alcohol solution, resulting in a 30% alcohol solution

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by VJesus12 » Fri Jul 09, 2021 11:30 am

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If a portion of a half water/half alcohol mix is replaced with 25% alcohol solution, resulting in a 30% alcohol solution, what percentage of the original alcohol was replaced?

A. 3%
B. 20%
C. 66%
D. 75%
E. 80%

Answer: E

Source: GMAT Club Tests
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Source: — Problem Solving |

VJesus12 wrote:
Fri Jul 09, 2021 11:30 am
If a portion of a half water/half alcohol mix is replaced with 25% alcohol solution, resulting in a 30% alcohol solution, what percentage of the original alcohol was replaced?

A. 3%
B. 20%
C. 66%
D. 75%
E. 80%

Answer: E

Source: GMAT Club Tests
Use Smart Numbers

Give \(100\) for the initial amount

Then you will have \(50-0.25x = 30 \Longrightarrow x=80\)

So \(\%\) is \(\dfrac{80}{100}\) is \(80\%\)
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