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As usual, do not agree with OA... 5^k

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Senior Manager
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As usual, do not agree with OA... 5^k [#permalink]  07 Oct 2007, 22:41
It is easy but I don't agree with OA
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Director
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Re: As usual, do not agree with OA... 5^k [#permalink]  07 Oct 2007, 23:07
Ferihere wrote:
It is easy but I don't agree with OA

EDITTED*

agree D,

1st SUFF, explanation below, miscalculated in the fisrt post.

2nd SUFF,

5^k=5 x 5^k - 2500

4 x 5^k=2500

5^k=5^4------------------> this is a specific value suff to answer if 5^k is less or more than 1000.

Last edited by IrinaOK on 08 Oct 2007, 00:07, edited 1 time in total.
Director
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Re: As usual, do not agree with OA... 5^k [#permalink]  07 Oct 2007, 23:37
Ferihere wrote:
It is easy but I don't agree with OA

D...

(1) 5^k-1 > 3000
=>5^k > 15000
SUFF

(2) 5^k-1 = 5^k - 500
=> 4*5^k-1= 500
=> k=4
5^4 = 625 i.e. < 1000
SUFF
Director
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Re: As usual, do not agree with OA... 5^k [#permalink]  08 Oct 2007, 00:11
(1) 5^k-1 > 3000
5^k > 15000. SUFF

(2) 5^k-1 = 5^k - 500
5^k / 5 = 5^k - 500
5^k = 5(5^k) - 2500
5 (5^k) - 5^k = 2500
4 (5^k) = 2500
5^k = 625...... suff.

got D as well but st. 1 and 2 are not leading to the same conclusion. this kind of question is not a gmat standard question and rare in real gmat.
Senior Manager
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Re: As usual, do not agree with OA... 5^k [#permalink]  08 Oct 2007, 00:26
Fistail wrote:
(1) 5^k-1 > 3000
5^k > 15000. SUFF

(2) 5^k-1 = 5^k - 500
5^k / 5 = 5^k - 500
5^k = 5(5^k) - 2500
5 (5^k) - 5^k = 2500
4 (5^k) = 2500
5^k = 625...... suff.

got D as well but st. 1 and 2 are not leading to the same conclusion. this kind of question is not a gmat standard question and rare in real gmat.

D....
Info (1) & Info (2) give TWO different answers

Agreed with Fistail - A real GMAT approach: Solutions are always unique!
Senior Manager
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AO is B, I dont undersand what is wrong. It is taken from DS 1000 set, section 17.

This is not the first time... with this sets
CEO
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Re: As usual, do not agree with OA... 5^k [#permalink]  08 Oct 2007, 10:29
Ferihere wrote:
It is easy but I don't agree with OA

What is the source of this problem? B/c this looks astonishingly similar to OG11 DS 131.

5^k>1000?

S1:

5^k-1>3000 ---> 5^k>15000. So this is suff.

S2:

5^k/5=5^k-500 (multiply the 5) ---> 5^k=5^k+1-2500. Here I just tried values.

k=4. Is the only one that works.

There is an alternative if u don't want to plug and chug.

5^k-5^k-1=500. 5^k-5^k(1/5) ---> 5^k(1-1/5) ---> 5^k(4/5) =500

5^k=625

So suff.

Ans is D.

If OA is B. Then S1 is written incorrectly. It should be written as 5^k+1>3000.
Director
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Re: As usual, do not agree with OA... 5^k [#permalink]  08 Oct 2007, 10:34
GMATBLACKBELT wrote:
There is an alternative if u don't want to plug and chug.

i heard plug before but not chug. what is it?
CEO
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Re: As usual, do not agree with OA... 5^k [#permalink]  08 Oct 2007, 10:46
Fistail wrote:
GMATBLACKBELT wrote:
There is an alternative if u don't want to plug and chug.

i heard plug before but not chug. what is it?

lol i dunno, i just remember using that term in my princeton review class for the SAT
Re: As usual, do not agree with OA... 5^k   [#permalink] 08 Oct 2007, 10:46
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