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# M25 Q30: Acid Solution Test

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M25 Q30: Acid Solution Test [#permalink]

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06 Feb 2011, 12:53
Hi I am a little confused by the explanation of this question and wondered if anyone could help?
Some part of a 50% solution of acid was replaced with an equal amount of 30% solution of acid. If, as a result, 40% solution of acid was obtained, what part of the original solution was replaced?
It then gives you answer options: 1/5, 1/4, 1/2. 3/4 and 4/5.

Any advice much appreciated.

K
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Joined: 20 Dec 2010
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Re: M25 Q30: Acid Solution Test [#permalink]

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06 Feb 2011, 14:21
Think of it as simple average, if I mix 50% with 30% and end up with 40%, I must have mixed equal parts of each fluid. If the final solution were 45%, I must have taken more of 50% than 30% and so on.

.5x + .3(1-x) = .4
.5x = .3 -.3x = .4
.2x = .1
2x = 1
x = 1/2

50%.........30%
.......40%......
10%.........10%

ratio 1:1, half of each
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Re: M25 Q30: Acid Solution Test   [#permalink] 06 Feb 2011, 14:21
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# M25 Q30: Acid Solution Test

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