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# How much water should be added to 10 liters of a

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VP
Joined: 22 Nov 2007
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How much water should be added to 10 liters of a [#permalink]  02 Mar 2008, 08:04
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How much water should be added to 10 liters of a 20%-solution of alcohol to reduce the concentration of alcohol in the solution by 75% ?
 25 liters
 27 liters
 30 liters
 32 liters
 35 liters
Director
Joined: 10 Sep 2007
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Re: Mixture [#permalink]  02 Mar 2008, 09:51
In original Content of 10 litre, there is 2 litre alcohol and 8 litre water.

Question ask to reduce concentration of alcohol to 5% (reduce concentration from 20% by 75%).

So lets assume X litre water is added.

So alcohol remains 2, water is 8+X and total content is 10+X.

Now 2*100/(10+X) = 5 => X = 30

VP
Joined: 22 Nov 2007
Posts: 1104
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Re: Mixture [#permalink]  02 Mar 2008, 09:58
abhijit_sen wrote:
In original Content of 10 litre, there is 2 litre alcohol and 8 litre water.

Question ask to reduce concentration of alcohol to 5% (reduce concentration from 20% by 75%).

So lets assume X litre water is added.

So alcohol remains 2, water is 8+X and total content is 10+X.

Now 2*100/(10+X) = 5 => X = 30

very quickly: 2/(10+x)=1/20, x=30
Re: Mixture   [#permalink] 02 Mar 2008, 09:58
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