How many ounces of water must be added to a 30-ounce solution that is 40 percent alcohol to dilute the solution to 25 percent alcohol?
*This question is included in Nova Math - Diagnostic: Test / Review, question #26

The solution is

Posted: 04/09/2012 06:37
I am poor at solving questions about solutions. Can someone help me? Appreciate.
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Posted: 04/09/2012 12:19
Dongxue, the solution for this "solution" problem is pretty extensive. "Solution" problems require you to understand % and master basic algebra. If you have any specific question, please post. We can only answer specific questions, not general tutoring questions.
Posted: 04/10/2012 00:24
How about this question? Can you explain it for me? Thanks
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Posted: 04/10/2012 01:18
Dongxue, the way it works is: tap the Solution button. Read it. If you don't understand a step, ask a specific question about the step or where you are stuck. Otherwise we will only repeat what's in there.
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Posted: 04/11/2012 02:15
Ok, Dongxue. Let's walk through this. First, you have to find how many ounces of alcohol in the first solution. Assume it's x ounces. So: x / (x+30) = 40%. Solve x from this equation.

Then, you will use x into the new solution:
x / (x + 30 ounces of original water + y additional ounces of water) = 25%
Here you will solve for y, the additional ounces of water.

I am sure you can get it!
Posted: 04/15/2012 07:18
But in the first solution, the amount of alcohol can be easy calculated by 30*40% since the total amount of solution is 30 ounces
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Posted: 04/16/2012 00:28
Dongxue, you caught my mistake in the explanation. You are right. I misread the question. In the first solution, the amount of alcohol is just 12 ounces. In the second solution, it becomes:
12 ounces / (30 ounces + added water) = 25%. We can solve for added water easily, which is 18.

Xie-xie for using our app.
Posted: 04/16/2012 00:41
Thanks. I finally get it. Actually I should xie-xie you for being so patient. Haha~
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Posted: 04/16/2012 01:13
Dongxue, bu keqi. If you are shooting for a high score, you should practice more. What grade are you and when are you planning to take the SAT? What would you purchase, and how much are you or your parents willing to spend for this kind of app? Did you consider private tutoring? You can email your answers to support@arcadiaprep.com

Posted: 12/05/2012 11:48
Relax, relax, relax. First, you have to find 40% of 30, which yields 12. So there are 12 ounces of alcohol in the solition. If this were to represent 25% of the solution, then simply multiply 12 by 4 and you get 48. Then subtract 30 from 48 and you get 18 ounces (C). It is long and confusing, but a little by little does the trick.
Posted: 12/01/2015 23:03
Why did u multiply by 4

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