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bblast: Legendary Member; Posts: 1077; Joined: Mon Dec 13, 2010 1:44 am; Thanked: 118 times; Followed by:33 members; GMAT Score:710

ALLIGATIONS GCLUB

by bblast » Sun May 22, 2011 2:04 am

If a portion of a half water/half alcohol mix is replaced with 25% alcohol solution, resulting in a 30% alcohol solution, what percentage of the original alcohol was replaced?

3
20
66
75
80

e

ANYBODY WITH ALLIGATIONS METHOD FOR THIS ONE. I cant recall how it worked.

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Frankenstein: Legendary Member; Posts: 1448; Joined: Tue May 17, 2011 9:55 am; Location: India; Thanked: 375 times; Followed by:53 members

by Frankenstein » Sun May 22, 2011 2:33 am

Hi,
concentration of liquid1 = 1/2
concentration of liquid2 = 1/4
concentration of mixture = 3/10

Ratio of volumes of liquid 1:liquid2 = (3/10-1/4) / (1/2-3/10) = (2/40)/(2/10) = 1:4
So, liquid 1 is 20 % of the mixture now. That means 80% of liquid1 is replaced by liquid 2

Hence, E

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bblast: Legendary Member; Posts: 1077; Joined: Mon Dec 13, 2010 1:44 am; Thanked: 118 times; Followed by:33 members; GMAT Score:710