It is currently 19 Oct 2017, 13:23

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

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

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

### Hide Tags

Intern
Joined: 13 Jan 2012
Posts: 41

Kudos [?]: 15 [1], given: 0

If n is a positive integer and k=5.1*10^n, what is the value [#permalink]

### Show Tags

21 Jan 2012, 09:01
1
KUDOS
6
This post was
BOOKMARKED
00:00

Difficulty:

45% (medium)

Question Stats:

66% (01:31) correct 34% (01:33) wrong based on 735 sessions

### HideShow timer Statistics

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

(1) 6,000 < k < 500,000
(2) k^2 = 2.601 * 10^9

[Reveal] Spoiler:
OG12: DS/151:
If n is a positive integer and k = 5.1 x 10^n, what is the value of k?

(1) 6000 < k < 500,000
(2) k^2 = 2.601 x 10^9

My Response:

(1) Solving for k by trying out n = 0,1,2,3 etc. we arrive at k = 51000 for n=4. SUFFICIENT.
(2) K could be 5.1 x 10^4 or -5.1 x 10^4. NOT SUFFICIENT.

Official Answer (OG12): D.
OG12 Explanation: 2nd statement implies k can only be 5.1 x 10^4. Why not (-5.1 x 10^4) ?
[Reveal] Spoiler: OA

Kudos [?]: 15 [1], given: 0

Math Expert
Joined: 02 Sep 2009
Posts: 41891

Kudos [?]: 128900 [0], given: 12183

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

### Show Tags

21 Jan 2012, 09:17
Expert's post
2
This post was
BOOKMARKED
fxsunny wrote:
OG12: DS/151:
If n is a positive integer and k = 5.1 x 10^n, what is the value of k?

(1) 6000 < k < 500,000
(2) k^2 = 2.601 x 10^9

My Response:

(1) Solving for k by trying out n = 0,1,2,3 etc. we arrive at k = 51000 for n=4. SUFFICIENT.
(2) K could be 5.1 x 10^4 or -5.1 x 10^4. NOT SUFFICIENT.

Official Answer (OG12): D.
OG12 Explanation: 2nd statement implies k can only be 5.1 x 10^4. Why not (-5.1 x 10^4) ?

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.

Hope it's clear.
_________________

Kudos [?]: 128900 [0], given: 12183

Intern
Joined: 13 Jan 2012
Posts: 41

Kudos [?]: 15 [1], given: 0

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

### Show Tags

21 Jan 2012, 22:41
1
KUDOS
Thanks, it is. I need to pay more attention to the question.

Kudos [?]: 15 [1], given: 0

Senior Manager
Joined: 15 Aug 2013
Posts: 302

Kudos [?]: 82 [0], given: 23

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

### Show Tags

31 Oct 2014, 14:30
Bunuel wrote:
fxsunny wrote:
OG12: DS/151:
If n is a positive integer and k = 5.1 x 10^n, what is the value of k?

(1) 6000 < k < 500,000
(2) k^2 = 2.601 x 10^9

My Response:

(1) Solving for k by trying out n = 0,1,2,3 etc. we arrive at k = 51000 for n=4. SUFFICIENT.
(2) K could be 5.1 x 10^4 or -5.1 x 10^4. NOT SUFFICIENT.

Official Answer (OG12): D.
OG12 Explanation: 2nd statement implies k can only be 5.1 x 10^4. Why not (-5.1 x 10^4) ?

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.

Hope it's clear.

Hi Bunuel,

If we weren't told that "n" is positive, wouldn't B still be sufficient? Isn't it true that whenever we take a square root, we always choose the positive value. Meaning, if we take a square root of 4, isn't the answer 2 and not +/- 2?

How is that any different than the k^2 value given above? Is it because we are working with a variable in k^2

Kudos [?]: 82 [0], given: 23

Math Expert
Joined: 02 Sep 2009
Posts: 41891

Kudos [?]: 128900 [1], given: 12183

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

### Show Tags

01 Nov 2014, 05:21
1
KUDOS
Expert's post
1
This post was
BOOKMARKED
russ9 wrote:
Bunuel wrote:
fxsunny wrote:
OG12: DS/151:
If n is a positive integer and k = 5.1 x 10^n, what is the value of k?

(1) 6000 < k < 500,000
(2) k^2 = 2.601 x 10^9

My Response:

(1) Solving for k by trying out n = 0,1,2,3 etc. we arrive at k = 51000 for n=4. SUFFICIENT.
(2) K could be 5.1 x 10^4 or -5.1 x 10^4. NOT SUFFICIENT.

Official Answer (OG12): D.
OG12 Explanation: 2nd statement implies k can only be 5.1 x 10^4. Why not (-5.1 x 10^4) ?

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.

Hope it's clear.

Hi Bunuel,

If we weren't told that "n" is positive, wouldn't B still be sufficient? Isn't it true that whenever we take a square root, we always choose the positive value. Meaning, if we take a square root of 4, isn't the answer 2 and not +/- 2?

How is that any different than the k^2 value given above? Is it because we are working with a variable in k^2

When the GMAT provides the square root sign for an even root, such as a square root, fourth root, etc. then the only accepted answer is the positive root.

That is:
$$\sqrt{9} = 3$$, NOT +3 or -3;
$$\sqrt[4]{16} = 2$$, NOT +2 or -2;

Notice that in contrast, the equation $$x^2 = 9$$ has TWO solutions, +3 and -3. Because $$x^2 = 9$$ means that $$x =-\sqrt{9}=-3$$ or $$x=\sqrt{9}=3$$.
_________________

Kudos [?]: 128900 [1], given: 12183

Senior Manager
Joined: 20 Aug 2015
Posts: 396

Kudos [?]: 336 [0], given: 10

Location: India
GMAT 1: 760 Q50 V44
If n is a positive integer and k=5.1*10^n, what is the value [#permalink]

### Show Tags

30 Dec 2015, 04:32
fxsunny wrote:
If n is a positive integer and k=5.1*10^n, what is the value of k?

(1) 6,000 < k < 500,000
(2) k^2 = 2.601 * 10^9

Given:
n is a positive integer.
k=5.1*10^n

Required: k = ?

Statement 1: 6,000 < k < 500,000
Since n is a positive integer, k can take the values 51, 510, 5100, 51000, 510000 etc.
Of these only one value lies in the range (6000, 500000)
Hence k = 51,000
SUFFICIENT

Statement 2: $$k^2$$ = 2.601 * $$10^9$$
This will give us 2 values of k, but we are concerned with the positive value only, since k cannot be negative as per the definition k = 5.1*$$10^n$$
SUFFICIENT

Option D
_________________

Reach out to us at bondwithus@gmatify.com

Kudos [?]: 336 [0], given: 10

SVP
Joined: 12 Sep 2015
Posts: 1797

Kudos [?]: 2458 [1], given: 356

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

### Show Tags

26 Jul 2016, 07:35
1
KUDOS
Expert's post
Top Contributor
2
This post was
BOOKMARKED
fxsunny wrote:
If n is a positive integer and k=5.1*10^n, what is the value of k?

(1) 6,000 < k < 500,000
(2) k² = 2.601 * 10^9

Target question: What is the value of k?

Given: n is a positive integer, and k = (5.1)x(10^n)
IMPORTANT: This since n can be ANY positive integer, there are several possible values of k.
They are: 51, 510, 5100, 51000, 510000, etc

Statement 1: 6,000 < k < 500,000
If we examine the possible values of k (51, 510, 5100, 51000, 510000, etc ), we can see that only ONE value (51,000) lies within the range defined by the inequality.
So, k must equal 51,000
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: k² = 2.601 x 10^9
If k²= 2.601 x 10^9, then EITHER k = √(2.601 x 10^9) OR k = -√(2.601 x 10^9). So, it appears that we cannot answer the target question.
HOWEVER, the question also tells us that k = 5.1 x 10^n, and since 5.1 x 10^n will always have a POSITIVE value, we know that k must be POSITIVE.
If k is POSITIVE, then k -√(2.601 x 10^9)
This means that k must equal √(2.601 x 10^9)
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

[Reveal] Spoiler:
D

Cheers,
Brent
_________________

Brent Hanneson – Founder of gmatprepnow.com

Kudos [?]: 2458 [1], given: 356

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16651

Kudos [?]: 273 [0], given: 0

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

### Show Tags

03 Sep 2017, 22:42
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 273 [0], given: 0

Re: If n is a positive integer and k=5.1*10^n, what is the value   [#permalink] 03 Sep 2017, 22:42
Display posts from previous: Sort by

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

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.