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## Question 20, section 17 of "lots of DS questions"

This topic has 1 expert reply and 3 member replies
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#### Question 20, section 17 of "lots of DS questions"

Tue Feb 13, 2007 1:00 pm

20. Is 5^k less than 1,000 ?
(1) 5^k-1>3000
(2) 5^k-1=5^k-500

B

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Stacey Koprince GMAT Instructor
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Wed Feb 14, 2007 8:05 pm
This is an OG question that has not been copied correctly (#131 in 11th edition).

Should be:

Is 5^k less than 1,000?
(1) 5^(k+1) > 3,000
(2) 5^(k-1) = (5^k) - 500

As I just wrote it above, the OA is B.

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banona Senior | Next Rank: 100 Posts
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Wed Feb 14, 2007 7:34 am
Hi,
I agree with amitamit2020 ; Answer should be D
Otherwise, check if expressions are as written in the original question and look at the source;

Neo2000 Legendary Member
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Tue Feb 13, 2007 9:07 pm
Can be answered using statement 2 alone

5^k -5^(k-1) = 500
By Law of Indices a^(m-n) = (a^m)/(a^n)

5^(k-1)(5 -1) = 500
4(5^(k-1)) = 500

Simplify to get value of k

amitamit2020 Junior | Next Rank: 30 Posts
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Wed Feb 14, 2007 3:23 am
I agree with Neo2000 that (2) is necessary and sufficient condiction to answer the quaestion. However stateembnt (1) can also provide sufficinet and necessary condiction to answer tha question because 5^(k-1) > 3000 means 5^k > 15000 > 1000, thus 5^k > 100. so the coreect answer to the quastion shoul be (D) rather than (B).

Pl. correct my understanding if found erronious.

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