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# certain quantity of 40% solution is replaced with 25%

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Current Student
Joined: 11 May 2008
Posts: 552
certain quantity of 40% solution is replaced with 25% [#permalink]

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28 Jul 2008, 10:54
certain quantity of 40% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?

(A) 1/4
(B) 1/3
(C) 1/2
(D) 2/3
(E) 3/4

i always screw up on such ones. pls guide....
what quantities to assume and how

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Senior Manager
Joined: 06 Apr 2008
Posts: 401

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28 Jul 2008, 11:02
arjtryarjtry wrote:
certain quantity of 40% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?

(A) 1/4
(B) 1/3
(C) 1/2
(D) 2/3
(E) 3/4

i always screw up on such ones. pls guide....
what quantities to assume and how

Let the quantity of solution be 1 and x be part of solution replaced

40% of (1-x) + 25% of x = 35% of 1

40 - 40x + 25x = 35

15x = 5

x = 1/3
Director
Joined: 20 Sep 2006
Posts: 639

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28 Jul 2008, 11:17
arjtryarjtry wrote:
certain quantity of 40% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?

(A) 1/4
(B) 1/3
(C) 1/2
(D) 2/3
(E) 3/4

i always screw up on such ones. pls guide....
what quantities to assume and how

40 (1-x) + 25 = 35

-40x = 35 - 65
x= 3/4 IMO E

EDITED: 40 (1-x) + 25x = 35 IMO B
Director
Joined: 20 Sep 2006
Posts: 639

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28 Jul 2008, 12:46
droopy57 wrote:
rao_1857 wrote:
arjtryarjtry wrote:
certain quantity of 40% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?

(A) 1/4
(B) 1/3
(C) 1/2
(D) 2/3
(E) 3/4

i always screw up on such ones. pls guide....
what quantities to assume and how

40 (1-x) + 25 = 35

-40x = 35 - 65
x= 3/4 IMO E

EDITED: 40 (1-x) + 25x = 35 IMO B

Why (1-x)?

certain quantity of 40% solution is replaced

total quantity = 1
quantity replaced = x

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: confusing %   [#permalink] 28 Jul 2008, 12:46
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# certain quantity of 40% solution is replaced with 25%

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