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If n is a positive integer and k = 5.1 x 10^n , what is the

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If n is a positive integer and k = 5.1 x 10^n , what is the [#permalink] New post 09 Mar 2011, 06:52
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If n is a positive integer and k = 5.1 x 10^n , what is the value of k ?

(1) 6,000 < k < 500,000
(2) k^2 = 2.601 * 10^9
[Reveal] Spoiler: OA

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Last edited by Bunuel on 18 Dec 2012, 07:21, edited 2 times in total.
Renamed the topic and edited the question.
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Re: Arithmetic properties [#permalink] New post 09 Mar 2011, 07:07
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Baten80 wrote:
If n is a positive integer and k = 5.1 x^n , what is the value of k ?
(1) 6,000 < k < 500,000
(2) k^2 = 2.601 * 10^9

I understand the official explanation. is there any other easy way?

Question should read:

If n is a positive integer and k = 5.1 * 10^n, what is the value of k ?

As n is a positive integer then k could be: 51, 510, 5,100, 51,000, ... Also note that no matter the value of n, k is always a positive number.

(1) 6,000 < k < 500,000 --> only one number from above is in this range: 51,000. Sufficient.

(2) k^2 = 2.601 * 10^9 --> we can solve quadratics to get two values of k positive and negative, but since given that k is positive then only the positive value of k will be valid. Sufficient.

Answer: D.
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Re: Arithmetic properties [#permalink] New post 09 Mar 2011, 07:31
Bunuel wrote:
Baten80 wrote:
If n is a positive integer and k = 5.1 x^n , what is the value of k ?
(1) 6,000 < k < 500,000
(2) k^2 = 2.601 * 10^9

I understand the official explanation. is there any other easy way?

Question should read:

If n is a positive integer and k = 5.1 * 10^n, what is the value of k ?

As n is a positive integer then k could be: 51, 510, 5,100, 51,000, ... Also note that no matter the value of n, k is always a positive number.

(1) 6,000 < k < 500,000 --> only one number from above is in this range: 51,000. Sufficient.

(2) k^2 = 2.601 * 10^9 --> we can solve quadratics to get two values of k positive and negative, but since given that k is positive then only the positive value of k will be valid. Sufficient.

Answer: D.

I corrected the original post.
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PSof OG solved by GC members: http://gmatclub.com/forum/collection-ps-with-solution-from-gmatclub-110005.html
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100 GMAT PREP Quantitative collection http://gmatclub.com/forum/gmat-prep-problem-collections-114358.html
Collections of work/rate problems with solutions http://gmatclub.com/forum/collections-of-work-rate-problem-with-solutions-118919.html
Mixture problems in a file with best solutions: http://gmatclub.com/forum/mixture-problems-with-best-and-easy-solutions-all-together-124644.html

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Re: If n is a positive integer and k = 5.1 x 10^n , what is the [#permalink] New post 21 Jun 2014, 18:59
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Re: If n is a positive integer and k = 5.1 x 10^n , what is the   [#permalink] 21 Jun 2014, 18:59
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