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# a 30% solution of alcohol is mixed with a 50% solution of

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Director
Joined: 12 Jun 2006
Posts: 524
a 30% solution of alcohol is mixed with a 50% solution of  [#permalink]

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20 Sep 2007, 05:27
a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.

2.0 liters
2.5 liters
2.7 liters
3.0 liters
3.2 liters

__________________________________________________________

I'm doing this and coming up empty.
30(L)/100 + 50(10-L)/100 = (10)45/100

--== Message from GMAT Club Team ==--

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If you would like to discuss this question please re-post it in the respective forum. Thank you!

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Director
Joined: 11 Jun 2007
Posts: 889
Re: what the %&*@ am i doing wrong? [Spoiler below red l  [#permalink]

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20 Sep 2007, 05:41
ggarr wrote:
a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.

2.0 liters
2.5 liters
2.7 liters
3.0 liters
3.2 liters

__________________________________________________________

I'm doing this and coming up empty.
30(L)/100 + 50(10-L)/100 = (10)45/100

It is actually quite simple. You want to find the ratio/weighted for each:

the answer should be B

dunno if I can explain this well.. there were these 'killer' notes that killersquirrel provided some time ago

30% + 50 % = 45% of a 10 liter solution
ratio of 30% : 50% ---> 1 : 3
so 30% = 1/4 or 25% of 10L solution = 2.5L
Director
Joined: 12 Jun 2006
Posts: 524

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20 Sep 2007, 05:50
beckee,

yeah. thanks. I have the notes. I'm just trying to solve the old fashioned way. i'd like to understand the traditional methods before moving on to the shortcuts

can anyone tell me what I'm doing wrong?
Quote:
a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.

2.0 liters
2.5 liters
2.7 liters
3.0 liters
3.2 liters

__________________________________________________________

I'm doing this and coming up empty.
30(L)/100 + 50(10-L)/100 = (10)45/100
Director
Joined: 11 Jun 2007
Posts: 889

### Show Tags

20 Sep 2007, 05:56
ggarr wrote:
beckee,

yeah. thanks. I have the notes. I'm just trying to solve the old fashioned way. i'd like to understand the traditional methods before moving on to the shortcuts

can anyone tell me what I'm doing wrong?
Quote:
a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.

2.0 liters
2.5 liters
2.7 liters
3.0 liters
3.2 liters

__________________________________________________________

I'm doing this and coming up empty.
30(L)/100 + 50(10-L)/100 = (10)45/100

I think you were getting there..but you have to set up simultaneous eqns. I would do it this way:

x + y = 10, or y = 10 - x

30x + 50 y = 45 (x + y)
30x + 50 (10-x) = 45 (10)
30x + 500 - 50x = 450
-20x = -50
20x = 50 -> 50/20
x = 2.5

see... still works out the old fashioned algebra way!
Intern
Joined: 11 Sep 2007
Posts: 11
Re: what the %&*@ am i doing wrong? [Spoiler below red l  [#permalink]

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20 Sep 2007, 12:11
beckee529 wrote:
ggarr wrote:
a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.

2.0 liters
2.5 liters
2.7 liters
3.0 liters
3.2 liters

__________________________________________________________

I'm doing this and coming up empty.
30(L)/100 + 50(10-L)/100 = (10)45/100

It is actually quite simple. You want to find the ratio/weighted for each:

the answer should be B

dunno if I can explain this well.. there were these 'killer' notes that killersquirrel provided some time ago

30% + 50 % = 45% of a 10 liter solution
ratio of 30% : 50% ---> 1 : 3 so 30% = 1/4 or 25% of 10L solution = 2.5L

This intrigues me - I don't understand the ratio of 1:3. Can anyone provide a link to the killer notes? I'd like to learn this.
Manager
Joined: 17 May 2007
Posts: 69

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20 Sep 2007, 12:20
someone had posted this file and i found it extremely helpful...took me all of 5 seconds to solve the problem
Attachments

File comment: mixture problems made easy

CEO
Joined: 21 Jan 2007
Posts: 2685
Location: New York City

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17 Oct 2007, 12:35
2
beckee529 wrote:
ggarr wrote:
beckee,

yeah. thanks. I have the notes. I'm just trying to solve the old fashioned way. i'd like to understand the traditional methods before moving on to the shortcuts

can anyone tell me what I'm doing wrong?
Quote:
a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.

2.0 liters
2.5 liters
2.7 liters
3.0 liters
3.2 liters

__________________________________________________________

I'm doing this and coming up empty.
30(L)/100 + 50(10-L)/100 = (10)45/100

I think you were getting there..but you have to set up simultaneous eqns. I would do it this way:

x + y = 10, or y = 10 - x

30x + 50 y = 45 (x + y)
30x + 50 (10-x) = 45 (10)
30x + 500 - 50x = 450
-20x = -50
20x = 50 -> 50/20
x = 2.5

see... still works out the old fashioned algebra way!

i like this way better. more intuitive
Director
Joined: 03 May 2007
Posts: 829
Schools: University of Chicago, Wharton School
Re: what the %&*@ am i doing wrong? [Spoiler below red l  [#permalink]

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17 Oct 2007, 17:04
ggarr wrote:
a 30% solution of alcohol is mixed with a 50% solution of alcohol to form a 10 liter solution of 45% alchohol. How much of the 30% solution was used.

2.0 liters
2.5 liters
2.7 liters
3.0 liters
3.2 liters

B. o.3x + 0.5 (1-x) = .45
x = 25%

so 30% alchohal has 25% of 10 lt = 2.5 lt.
VP
Joined: 09 Jul 2007
Posts: 1081
Location: London

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17 Oct 2007, 19:19
gowani wrote:
someone had posted this file and i found it extremely helpful...took me all of 5 seconds to solve the problem

Appreciate gowani,
it will take me now 3 seconds to solve this kinda PS!
Non-Human User
Joined: 09 Sep 2013
Posts: 7773
Re: a 30% solution of alcohol is mixed with a 50% solution of  [#permalink]

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06 Apr 2017, 13:24
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--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

_________________
Re: a 30% solution of alcohol is mixed with a 50% solution of &nbs [#permalink] 06 Apr 2017, 13:24
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