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How much pure alcohol should be added to 400ml of a 15% solu

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Manager
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How much pure alcohol should be added to 400ml of a 15% solu [#permalink] New post 02 Dec 2009, 00:21
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Difficulty:

  25% (medium)

Question Stats:

82% (02:25) correct 18% (01:18) wrong based on 55 sessions
How much pure alcohol should be added to 400ml of a 15% solution to make the strength of solution 32%?

A. 100 ml
B. 60 ml
C. 120 ml
D. 130 ml
E. 150 ml
[Reveal] Spoiler: OA
Senior Manager
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Joined: 30 Aug 2009
Posts: 290
Location: India
Concentration: General Management
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Re: Alcohol [#permalink] New post 02 Dec 2009, 00:35
kirankp wrote:
How much pure alcohol should be added to 400ml of a 15% solution to make the strength of solution 32%?

A)100 ml
B) 60 ml
C)120 ml
D)130 ml
E)150 ml


400ml has 15% alcohol i.e 60ml . This means we have 340ml of water or the liquid with which alcohol is mixed
Let V be the volume of alcohol added to make the strength 32%
then V/340+V = 32/100. solving this we get V as 160ml

so we need to add 160 -60 = 100ml of alcohol

A-100ml
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Re: Alcohol [#permalink] New post 02 Dec 2009, 13:28
Here's how I did it:

(400)(.15) = 60 mL of Alcohol

.32 = \frac{60+x}{400+x}

(.32)(400+x)=60+x

128+.32x=60+x

68=.68x

x=100
Manager
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Re: Alcohol [#permalink] New post 02 Dec 2009, 22:17
we can also go by answer choices

Tke 100 ml for eg

400 (old)+100 (new concentr)ml

500*32/100 = 160 ml (60ml is de old concentration +100 ml (newly added)

Let me know if im wrong :roll:

Cheers,
Raghav
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Re: Alcohol [#permalink] New post 02 Dec 2009, 22:25
raghavs wrote:
we can also go by answer choices

Tke 100 ml for eg

400 (old)+100 (new concentr)ml

500*32/100 = 160 ml (60ml is de old concentration +100 ml (newly added)

Let me know if im wrong :roll:

Cheers,
Raghav


yes we can go by answer choices as well....but in GMAT we will see questions having values either in ascending or descending order unlike the options in the question here. Plugging in/POE is always suggested to be done taking the middle option first and then proceed.
I feel taking answer choices will take more time to solve this question.
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Re: Alcohol [#permalink] New post 17 Dec 2009, 03:23
kirankp wrote:
How much pure alcohol should be added to 400ml of a 15% solution to make the strength of solution 32%?

A)100 ml
B) 60 ml
C)120 ml
D)130 ml
E)150 ml


let xml is added
15% of 400=60 ml
after addition
(60+x)/(400+x)=32%
solving x=100 ml
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Re: Alcohol   [#permalink] 17 Dec 2009, 03:23
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