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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]

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New post 09 Mar 2011, 07:52
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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, 08:21, edited 2 times in total.
Renamed the topic and edited the question.
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Re: Arithmetic properties [#permalink]

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New post 09 Mar 2011, 08:07
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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]

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New post 09 Mar 2011, 08:31
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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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
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Re: If n is a positive integer and k = 5.1 x 10^n , what is the [#permalink]

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Re: If n is a positive integer and k = 5.1 x 10^n , what is the [#permalink]

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New post 21 Jul 2015, 20:38
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If n is a positive integer and k = 5.1 x 10^n , what is the valu [#permalink]

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New post 23 Jul 2015, 13:47
Actually the answer D is correct.

Allow me to explain. As n is a positive integer. The values of k will be

n=1 --> 51
n+2 --> 510
n+3 --> 5,100
n+4 --> 51,000
n+5 --> 510,000


The inequality,although very wide,tells us about the only possible value of k which is 51,000. As 5100 is less than 6000 and 510,000 is more than 500,000.

Statement B is sufficient on its own. Should give a positive and negative value of K. But the question stem tells us that K is positive.

Hope this helps
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Re: If n is a positive integer and k = 5.1 x 10^n , what is the [#permalink]

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New post 16 Jul 2016, 06:34
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.


could you please explain the solution of statement 2
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Re: If n is a positive integer and k = 5.1 x 10^n , what is the [#permalink]

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New post 16 Jul 2016, 08:38
Expert's post
Maruf Iqbal wrote:
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.


could you please explain the solution of statement 2


\(k^2 = 2.601 * 10^9 = 2601*10^6 = 51^2*(10^3)^2\)

\(k= \sqrt{51^2*(10^3)^2}=51*10^3=51000\)
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Please read this: All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
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Re: If n is a positive integer and k = 5.1 x 10^n , what is the   [#permalink] 16 Jul 2016, 08:38
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