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Good question. When I first tried it, I kind of overlooked the word extracted. Once I realized the answer i came up with was not an answer choice...I decided to look at the question again. I need to figure out how to overcome this problem I sometimes have with reading a question and not catching certain key words.

I would suggest a generalized strategy: 1) reading the question in parts and not the whole in one go. 2) writing down the necessary numbers to make it simpler (i.e. converting the English into Numbers). In the above example, the key is to understand that 'sand' should not be extracted, which means that the 'sand' quantity in the mixture will not change. Only the proportion(% in terms of the mixture) will change. First 'sand' was 20% of the mixture i.e. 40lbs. Later-on this 40lbs 'sand' becomes 25% of the mixture. Now the rest 75% of the mixture will be 120lbs of husk. Which is a reduction of 40lbs of 'husk', which is your answer.

80% of 200 = 160 lb of husk ---> Total Husk in 200 lb. 75% concentration of total husk = 75% of 160 lb = (3/4) * 160 = 120

Total amount to be extracted = Initial Amount of Husk - 75% concentration of Husk Total amount to be extracted = 160 lb - 120 lb = 40 lb
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I would suggest a generalized strategy: 1) reading the question in parts and not the whole in one go. 2) writing down the necessary numbers to make it simpler (i.e. converting the English into Numbers). In the above example, the key is to understand that 'sand' should not be extracted, which means that the 'sand' quantity in the mixture will not change. Only the proportion(% in terms of the mixture) will change. First 'sand' was 20% of the mixture i.e. 40lbs. Later-on this 40lbs 'sand' becomes 25% of the mixture. Now the rest 75% of the mixture will be 120lbs of husk. Which is a reduction of 40lbs of 'husk', which is your answer.

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
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Re: If 200 lb of a mixture contain 80% husk and 20% sand. Then [#permalink]

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18 Apr 2014, 20:25

Total=200lb

Husk=160 Other=40

Consider X is taken out.

(160-X) = .75 (200-X) {Since the new solution has 75% conc.}

X=40
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Rgds, TGC! _____________________________________________________________________ I Assisted You => KUDOS Please _____________________________________________________________________________

Re: If 200 lb of a mixture contain 80% husk and 20% sand. Then [#permalink]

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28 May 2014, 18:13

Easy approach:

From the question you know that Husk = 160lbs (80% of 200) Sand = 40lbs (20% of 200)

After removing some Husk the concentration will be 75%. We need to find how much Husk to remove

Remember that the quantity of sand doesn't change, we still have 40lbs of sand, but now they represent 25% of the new mix. If 25% = 40lbs, 75% equals 120lbs (simple math)

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