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# A tank contains 10,000 gallons of a solution that is 5 %

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A tank contains 10,000 gallons of a solution that is 5 % [#permalink]  11 Oct 2005, 02:04
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A tank contains 10,000 gallons of a solution that is 5 percent sodium chloride by volume. If 2,500 gallons of water evaporate from the tank, the remaining solution will be approximately what percent sodium chloride?

(A) 1.25%
(B) 3.75%
(C) 6.25%
(D) 6.67%
(E) 11.7%
[Reveal] Spoiler: OA
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Re: PS - Percents OG11 [#permalink]  11 Oct 2005, 14:23
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Should be D

Original =10,000 ----> sodium chloride = 5% ie 500
New = 10,000-2,500 = 7500.

New % = (500/7500) * 100

= 6.67%

nero44 wrote:
I think my brain evaporated, because I dont even get any of the solutions given...

A tank contains 10,000 gallons of a solution that is 5 percent sodium chloride by volume. If 2,500 gallons of water evaporate from the tank, the remaining solution will be approximately what percent sodium chloride?

(A) 1.25%
(B) 3.75%
(C) 6.25%
(D) 6.67%
(E) 11.7%
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I got 6.67%

10000 gallons solution has
500 gallons sodium chloride
9500 gallons water

=> 2500 gallons water evaporates
=> 7000 gallons water remains

hence, concentration of sodium chloride is 500/7500 = 6.67%
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Re: A tank contains 10,000 gallons of a solution that is 5% [#permalink]  03 Mar 2012, 15:45
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Expert's post
Minhphuoc wrote:
A tank contains 10,000 gallons of a solution that is 5 percent sodium chloride by volume. If 2,500 gallons of water evaporate from the tank, the remaining solution will be approximately what percent sodium chloride?

(A) 1.25%
(B) 3.75%
(C) 6.25%
(D) 6.67%
(E) 11.7%

hi, everybody,

Sorry for raised this question again, but I a little bit confused with the question by itself.

Is that correct that if I interpret the question statement 'the remaining solution' (A) will be approximately what percent (B) 'sodium chloride'? as A=%B?

It makes me generate wrong answer!

Thanks

"The remaining solution will be approximately what percent sodium chloride?" means: what percent of the remaining solution is sodium chloride. Now, since the remaining solution is 10,000-2,500=7,500 gallons and sodium chloride is 500 gallons (5% of initial solution of 10,000 gallons) then sodium chloride is 500/7,500*100=~6.66% of the remaining solution of 7,500 gallons.

Hope it's clear.
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Re: A tank contains 10,000 gallons of a solution that is 5 % [#permalink]  20 Jan 2015, 02:18
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Expert's post
arshu27 wrote:
Bunuel wrote:
Minhphuoc wrote:
A tank contains 10,000 gallons of a solution that is 5 percent sodium chloride by volume. If 2,500 gallons of water evaporate from the tank, the remaining solution will be approximately what percent sodium chloride?

(A) 1.25%
(B) 3.75%
(C) 6.25%
(D) 6.67%
(E) 11.7%

hi, everybody,

Sorry for raised this question again, but I a little bit confused with the question by itself.

Is that correct that if I interpret the question statement 'the remaining solution' (A) will be approximately what percent (B) 'sodium chloride'? as A=%B?

It makes me generate wrong answer!

Thanks

"The remaining solution will be approximately what percent sodium chloride?" means: what percent of the remaining solution is sodium chloride. Now, since the remaining solution is 10,000-2,500=7,500 gallons and sodium chloride is 500 gallons (5% of initial solution of 10,000 gallons) then sodium chloride is 500/7,500*100=~6.66% of the remaining solution of 7,500 gallons.

Hope it's clear.

Hi Bunuel,

As you said the question asks 'what percent of the remaining solution is sodium chloride'.

After evaporation,

volume of water=7500 gallons

volume of sodium chloride =500(no change)

total volume of the SOLUTION(water and sodium chloride)=7500+500

therfore 500/8000*100=6.25

Even though this does not match the right answer my doubt is why are you not taking the total which includes both? Initially we did take solution to be water and sodium chloride as one.The question uses the term 'remaining solution'. Could you please help me clear this confusion?

After 2,500 gallons of water evaporates from the tank, we are left with 7,500 gallons of solution, which includes 500 gallons of sodium chloride.
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Re: PS - Percents OG11 [#permalink]  11 Oct 2005, 02:48
nero44 wrote:
I think my brain evaporated, because I dont even get any of the solutions given...

A tank contains 10,000 gallons of a solution that is 5 percent sodium chloride by volume. If 2,500 gallons of water evaporate from the tank, the remaining solution will be approximately what percent sodium chloride?

(A) 1.25%
(B) 3.75%
(C) 6.25%
(D) 6.67%
(E) 11.7%

there're 5%*10,000(= 500 gallons) of NaCl in the solution
===> there're 9,500 (=10,000-500) gallons of water in the solution.
after 2,500 gallons of water evaporate, there's 7,000 gallons of water left ===> the percentage of NaCl is 500 gallons NaCl/ (500+7,000) ( this is the volume of the solution) *100%= 6,67% . It's D.
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Re: A tank contains 10,000 gallons of a solution that is 5% [#permalink]  03 Mar 2012, 10:14
hi, everybody,

Sorry for raised this question again, but I a little bit confused with the question by itself.

Is that correct that if I interpret the question statement 'the remaining solution' (A) will be approximately what percent (B) 'sodium chloride'? as A=%B?

It makes me generate wrong answer!

Thanks
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Re: A tank contains 10,000 gallons of a solution that is 5 % [#permalink]  27 Mar 2012, 21:30
I'm really slow with math, need suggestions.

I solved this question in 2 minutes 45 seconds and got the correct answer, but obviously my time was too slow. Any suggestions for how to complete this quickly? The slowest part for me was calculating what 500/7500 is.

This was my process:
500/7500 = 5/75 = 1/15.

Long division 1/15 = 6.6% (then looked for correct answer).

Any suggestions for how to do that calculation faster (beyond just memorizing) would be great!
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Re: A tank contains 10,000 gallons of a solution that is 5 % [#permalink]  02 Oct 2013, 13:33
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Re: A tank contains 10,000 gallons of a solution that is 5 % [#permalink]  12 Oct 2013, 01:50
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Status: Math is psycho-logical
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A tank contains 10,000 gallons of a solution that is 5 % [#permalink]  19 Jan 2015, 08:49
Hey,

I have two questions on this problem:
1) Saying that it is a "solution" we should assume that there are at least 2 elements in it?
2) Because it says 2500 gallons of water evaporated, we should assume that only water evaporated, so the sodium chloride has remained intact?

That because if you think that the solution is the "sodium chloride", then the % should remain the same (5%) after some amount of the solution is gone. Which would make you answer # B. Even though this is obiously wrong as the % would be the same..

It does make sense that you are supposed to understand that there are 2 elements in this solution, and sodium chloride has remained intact, since it was only water that evaporated, but I guess in this case they could have made it a bit more obvious by saying "If 2,500 gallons that consist only of water evaporate from the tank ", then you would get the correct answer quite easily...

Sorry, it just seems a bit ridiculous that they trick you for silly reasons..
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Re: A tank contains 10,000 gallons of a solution that is 5 % [#permalink]  19 Jan 2015, 09:40
Bunuel wrote:
Minhphuoc wrote:
A tank contains 10,000 gallons of a solution that is 5 percent sodium chloride by volume. If 2,500 gallons of water evaporate from the tank, the remaining solution will be approximately what percent sodium chloride?

(A) 1.25%
(B) 3.75%
(C) 6.25%
(D) 6.67%
(E) 11.7%

hi, everybody,

Sorry for raised this question again, but I a little bit confused with the question by itself.

Is that correct that if I interpret the question statement 'the remaining solution' (A) will be approximately what percent (B) 'sodium chloride'? as A=%B?

It makes me generate wrong answer!

Thanks

"The remaining solution will be approximately what percent sodium chloride?" means: what percent of the remaining solution is sodium chloride. Now, since the remaining solution is 10,000-2,500=7,500 gallons and sodium chloride is 500 gallons (5% of initial solution of 10,000 gallons) then sodium chloride is 500/7,500*100=~6.66% of the remaining solution of 7,500 gallons.

Hope it's clear.

Hi Bunuel,

As you said the question asks 'what percent of the remaining solution is sodium chloride'.

After evaporation,

volume of water=7500 gallons

volume of sodium chloride =500(no change)

total volume of the SOLUTION(water and sodium chloride)=7500+500

therfore 500/8000*100=6.25

Even though this does not match the right answer my doubt is why are you not taking the total which includes both? Initially we did take solution to be water and sodium chloride as one.The question uses the term 'remaining solution'. Could you please help me clear this confusion?
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Re: A tank contains 10,000 gallons of a solution that is 5 % [#permalink]  21 Jan 2015, 12:15
thank you Bunuel. got it!
Re: A tank contains 10,000 gallons of a solution that is 5 %   [#permalink] 21 Jan 2015, 12:15
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