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# Some part of the 50% solution of acid was replaced with the

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Manager
Joined: 21 Feb 2008
Posts: 87
Schools: UCLA Anderson '12
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Some part of the 50% solution of acid was replaced with the [#permalink]  21 Oct 2008, 10:41
Some part of the 50% solution of acid was replaced with the equal amount of 30% solution of acid. As a result, 40% solution of acid was obtained. What part of the original solution was replaced?

A. $$\frac{1}{5}$$

B. $$\frac{1}{4}$$

C. $$\frac{1}{2}$$

D. $$\frac{3}{4}$$

E. $$\frac{4}{5}$$

Answer is C. It's relatively easy to understand why 1/2 is correct but I can't logically put an equation together to solve the question.
SVP
Joined: 07 Nov 2007
Posts: 1824
Location: New York
Followers: 29

Kudos [?]: 564 [0], given: 5

Re: Difficult Ratio question [#permalink]  21 Oct 2008, 12:16
duuuma wrote:
Some part of the 50% solution of acid was replaced with the equal amount of 30% solution of acid. As a result, 40% solution of acid was obtained. What part of the original solution was replaced?

A. $$\frac{1}{5}$$

B. $$\frac{1}{4}$$

C. $$\frac{1}{2}$$

D. $$\frac{3}{4}$$

E. $$\frac{4}{5}$$

Answer is C. It's relatively easy to understand why 1/2 is correct but I can't logically put an equation together to solve the question.

x is part of solution replaced

0.5 (1-x) +0.3*x = 0.4*1

x=1/2
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SVP
Joined: 29 Aug 2007
Posts: 2493
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Kudos [?]: 578 [0], given: 19

Re: Difficult Ratio question [#permalink]  21 Oct 2008, 13:10
0.5 (1-X) + 0.3X = 0.4
X = 1/2

CANNOT ADD ANYTHING TO ABOVE SOL.
_________________
Manager
Joined: 21 Feb 2008
Posts: 87
Schools: UCLA Anderson '12
Followers: 4

Kudos [?]: 21 [0], given: 2

Re: Difficult Ratio question [#permalink]  21 Oct 2008, 13:48
Not sure I understand your comment. What do you mean by, "cannot add anything..."?
GMAT TIGER wrote:
0.5 (1-X) + 0.3X = 0.4
X = 1/2

CANNOT ADD ANYTHING TO ABOVE SOL.
SVP
Joined: 29 Aug 2007
Posts: 2493
Followers: 59

Kudos [?]: 578 [0], given: 19

Re: Difficult Ratio question [#permalink]  21 Oct 2008, 15:39
duuuma wrote:
Not sure I understand your comment. What do you mean by, "cannot add anything..."?
GMAT TIGER wrote:
0.5 (1-X) + 0.3X = 0.4
X = 1/2

CANNOT ADD ANYTHING TO ABOVE SOL.

I meant "CANNOT ADD ANYTHING TO THE ABOVE SOL.by "x2suresh". Is it clear now, "duuuma"?
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Manager
Joined: 21 Feb 2008
Posts: 87
Schools: UCLA Anderson '12
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Kudos [?]: 21 [0], given: 2

Re: Difficult Ratio question [#permalink]  21 Oct 2008, 15:49
I'm guessing you meant that you agree with his solution and cannot add anything on top of that? Makes sense - thanks

GMAT TIGER wrote:

I meant "CANNOT ADD ANYTHING TO THE ABOVE SOL.by "x2suresh". Is it clear now, "duuuma"?
SVP
Joined: 29 Aug 2007
Posts: 2493
Followers: 59

Kudos [?]: 578 [0], given: 19

Re: Difficult Ratio question [#permalink]  21 Oct 2008, 17:31
duuuma wrote:
I'm guessing you meant that you agree with his solution and cannot add anything on top of that? Makes sense - thanks

GMAT TIGER wrote:

I meant "CANNOT ADD ANYTHING TO THE ABOVE SOL.by "x2suresh". Is it clear now, "duuuma"?

you got it, duuuma.
_________________
Re: Difficult Ratio question   [#permalink] 21 Oct 2008, 17:31
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