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6 litres of pure acid is added to 10 l of a mixture of acid

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Ravi 1596 Newbie | Next Rank: 10 Posts
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6 litres of pure acid is added to 10 l of a mixture of acid

Post Mon Jul 24, 2017 10:38 am
6 litres of pure acid is added to 10 l of a mixture of acid and water with 40% acid.What is the percentage of acid in the new solution

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Post Tue Jul 25, 2017 2:26 pm
rsarashi wrote:
Hello Experts,

What am I doing wrong?

10L mixture is given, so x be the acid in this mixture.

Now 6L of pure acid is added. So the equation would be like below.

(x+6/10+6)*100 = 40/100

Please explain if I understood the question in wrong way.

Thanks.
That calculation assumes that the NEW solution is 40% acid (AFTER the 6 liters of pure acid is added), whereas the question tells us that that ORIGINAL solution is 40% acid.

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Post Wed Jul 26, 2017 3:23 pm
Ravi 1596 wrote:
6 litres of pure acid is added to 10 l of a mixture of acid and water with 40% acid.What is the percentage of acid in the new solution
The current mixture contains 10 x 0.4 = 4 liters of acid and 6 liters of water. If 6 liters of acid are added, the amount of acid is now 10 liters and the total solution is now 16 liters.

Thus, the percentage of acid is 10/16 x 100 = 62.5%.

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Post Tue Jul 25, 2017 2:26 pm
rsarashi wrote:
Hello Experts,

What am I doing wrong?

10L mixture is given, so x be the acid in this mixture.

Now 6L of pure acid is added. So the equation would be like below.

(x+6/10+6)*100 = 40/100

Please explain if I understood the question in wrong way.

Thanks.
That calculation assumes that the NEW solution is 40% acid (AFTER the 6 liters of pure acid is added), whereas the question tells us that that ORIGINAL solution is 40% acid.

_________________
Brent Hanneson – Founder of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Check out the online reviews of our course
Come see all of our free resources

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Thanked by: rsarashi
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Post Wed Jul 26, 2017 3:23 pm
Ravi 1596 wrote:
6 litres of pure acid is added to 10 l of a mixture of acid and water with 40% acid.What is the percentage of acid in the new solution
The current mixture contains 10 x 0.4 = 4 liters of acid and 6 liters of water. If 6 liters of acid are added, the amount of acid is now 10 liters and the total solution is now 16 liters.

Thus, the percentage of acid is 10/16 x 100 = 62.5%.

_________________

Scott Woodbury Stewart Founder & CEO
GMAT Quant Self-Study Course - 500+ lessons 3000+ practice problems 800+ HD solutions
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rsarashi Master | Next Rank: 500 Posts Default Avatar
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Post Thu Jul 27, 2017 8:56 am
Quote:
That calculation assumes that the NEW solution is 40% acid (AFTER the 6 liters of pure acid is added), whereas the question tells us that that ORIGINAL solution is 40% acid.
Hi Brent ,

Thank you so much for your help sir.

All clear.

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rsarashi Master | Next Rank: 500 Posts Default Avatar
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Post Tue Jul 25, 2017 9:49 am
Hello Experts,

What am I doing wrong?

10L mixture is given, so x be the acid in this mixture.

Now 6L of pure acid is added. So the equation would be like below.

(x+6/10+6)*100 = 40/100

Please explain if I understood the question in wrong way.

Thanks.

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Post Mon Jul 24, 2017 5:15 pm
Hi Ravi 1596,

Both Brent and Mitch have explained the math behind this question, so I won't rehash any of that here. For future reference though, when posting GMAT questions, you should make sure to post the FULL question (with the 5 answer choices). Sometimes the answer choices are designed to give you a potential 'shortcut' (or help you to avoid a 'long' math approach), so as you continue to study, you should look to take advantage of ALL of the information that you're given to work with - and giving the other site members and Experts access to the full question can help us to show you all of those shortcuts.

GMAT assassins aren't born, they're made,
Rich

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Contact Rich at Rich.C@empowergmat.com

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