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4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52

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Manager
Joined: 10 Feb 2011
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4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52 [#permalink]

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15 Mar 2011, 16:40
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25% (01:41) correct 75% (00:45) wrong based on 4 sessions

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4. (GC) If 25/(x/5) = (1/25)/125 then x = ?
(A) 5^-2
(B) 5^2
(C) 5^3
(D) 5^8
(E) 5^11
[Reveal] Spoiler: OA

Last edited by banksy on 16 Mar 2011, 09:00, edited 1 time in total.
Intern
Joined: 06 Feb 2011
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Kudos [?]: 3 [0], given: 3

Re: 4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52 [#permalink]

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15 Mar 2011, 18:37
rewrite as:
25*(5/x) = (1/25)*(1/125)
(5^3)/x = (1/(5^2))*(1/(5^3))
1/x = (1/(5^2))*(1/(5^3))*(1/(5^3))
1/x = 1/(5^7)
x = (5^7)

Where did you get that answer?
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Joined: 16 Nov 2010
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Location: United States (IN)
Concentration: Strategy, Technology
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Kudos [?]: 491 [0], given: 36

Re: 4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52 [#permalink]

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15 Mar 2011, 21:49
=> 125/x = 1/25 * 1/125

=> x = 5^3 * 5^2 * 5^3 => x = 5^8

I think the answer choices should read 5^-2, 5^2, 5^3, 5^8, 5^11.

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Intern
Joined: 06 Feb 2011
Posts: 9
Followers: 0

Kudos [?]: 3 [0], given: 3

Re: 4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52 [#permalink]

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16 Mar 2011, 05:11
Manager
Joined: 03 Jun 2010
Posts: 138
Location: Dubai, UAE
Schools: IE Business School, Manchester Business School, HEC Paris, Rotterdam School of Management, Babson College
Followers: 2

Kudos [?]: 4 [0], given: 4

Re: 4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52 [#permalink]

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16 Mar 2011, 05:21
Why isnt it

25/(x/5)=(1/25)/125
25*5/x=1/25*1/125
125/x=1/(125)(25)
1/x=1/25
x=25
x=5^2
Math Forum Moderator
Joined: 20 Dec 2010
Posts: 2021
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Kudos [?]: 1625 [0], given: 376

Re: 4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52 [#permalink]

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16 Mar 2011, 05:36
scbguy wrote:
Why isnt it

25/(x/5)=(1/25)/125
25*5/x=1/25*1/125
125/x=1/(125)(25)
1/x=1/25
x=25
x=5^2

$$\frac{125}{x} = \frac{1}{125*25}$$

If we cross multiply;

$$x = 125*125*25$$

$$x = 5^3*5^3*5^2$$

$$x = 5^{(3+3+2)} = 5^8$$
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Manager
Joined: 03 Jun 2010
Posts: 138
Location: Dubai, UAE
Schools: IE Business School, Manchester Business School, HEC Paris, Rotterdam School of Management, Babson College
Followers: 2

Kudos [?]: 4 [0], given: 4

Re: 4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52 [#permalink]

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16 Mar 2011, 05:59
got it thanks , i thought we could cancel out 125
Re: 4. (GC) If 25/(x/5) = (1/25)/125 then x = ? (A) 5-2 (B) 52   [#permalink] 16 Mar 2011, 05:59
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