GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 15 Jul 2018, 12:08

### 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

# What is the value of the integer n? (1) n(n + 2) = 15 (2) (n

Author Message
TAGS:

### Hide Tags

Manager
Joined: 28 Aug 2010
Posts: 234
What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

Updated on: 10 Jul 2013, 01:54
1
13
00:00

Difficulty:

45% (medium)

Question Stats:

64% (00:53) correct 36% (00:56) wrong based on 807 sessions

### HideShow timer Statistics

What is the value of the integer n?

(1) n(n + 2) = 15
(2) (n + 2)^n = 125

I am not sure if the given ans is right

_________________

Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html
-------------------------------------------------------------------------------------------------
Ajit

Originally posted by ajit257 on 30 Dec 2010, 17:27.
Last edited by Bunuel on 10 Jul 2013, 01:54, edited 1 time in total.
Edited the OA.
Math Expert
Joined: 02 Sep 2009
Posts: 46991
Re: What is the value of the integer n....Exponents [#permalink]

### Show Tags

30 Dec 2010, 17:45
5
4
ajit257 wrote:
What is the value of the integer n?

(1) n(n + 2) = 15
(2) (n + 2)^n = 125

I am not sure if the given ans is right

What is the value of the integer n?

(1) n(n + 2) = 15 --> $$n^2+2n-15=0$$ --> $$(n+5)(n-3)=0$$ --> $$n=-5$$ or $$n=3$$. Not sufficient.

(2) (n + 2)^n = 125 --> as $$n$$ is an integer then $$(n + 2)^n=125^1=5^3$$ (125 can be written as integer^integer only in those two ways), only $$n=3$$ works: $$(2+3)^3=5^3=125$$. Sufficient.

_________________
##### General Discussion
Manager
Joined: 28 Aug 2010
Posts: 234
Re: What is the value of the integer n....Exponents [#permalink]

### Show Tags

30 Dec 2010, 17:53
1
Bunuel,
Thanks for the confirmation. I got the same. The given ans is wrong ...should be B.
_________________

Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html
-------------------------------------------------------------------------------------------------
Ajit

Intern
Joined: 22 Oct 2010
Posts: 7
Re: What is the value of the integer n....Exponents [#permalink]

### Show Tags

31 Dec 2010, 18:04
1
C it is

statment 2) is not sufficient coz N can be a decimal value

from statement 1) we know that N= -5 or 3
by sustituting these values in statement 2), we know that N=3
Intern
Joined: 23 Nov 2010
Posts: 6
Location: India
Re: What is the value of the integer n....Exponents [#permalink]

### Show Tags

01 Jan 2011, 01:28
girishkakkar wrote:
C it is

statment 2) is not sufficient coz N can be a decimal value

from statement 1) we know that N= -5 or 3
by sustituting these values in statement 2), we know that N=3

The question clearly states
"What is the value of the integer n?"

So the answer should be B.
Intern
Joined: 22 Oct 2010
Posts: 7
Re: What is the value of the integer n....Exponents [#permalink]

### Show Tags

01 Jan 2011, 08:12
but talking about statement 2), cant value of N be 3 or ANY decimal number? Since it is NOT stated in the question that "N is an integer". Correct me if I am wrong.
Math Expert
Joined: 02 Sep 2009
Posts: 46991
Re: What is the value of the integer n....Exponents [#permalink]

### Show Tags

01 Jan 2011, 08:18
girishkakkar wrote:
but talking about statement 2), cant value of N be 3 or ANY decimal number? Since it is NOT stated in the question that "N is an integer". Correct me if I am wrong.

Question is: What is the value of the integer n? So the stem explicitly says that n is an integer.
_________________
Director
Status: No dream is too large, no dreamer is too small
Joined: 14 Jul 2010
Posts: 544
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

04 Jan 2012, 10:18
Manager
Joined: 29 Jul 2011
Posts: 97
Location: United States
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

04 Jan 2012, 14:14
Agree with Buneul. If n is integer, them then S2 has to be an integer.

1. Clearly insufficient, two roots = -5,3
2. Since n is integer, only n that satisfies this equation is n = 3. Sufficient

+B.
_________________

I am the master of my fate. I am the captain of my soul.
Please consider giving +1 Kudos if deserved!

DS - If negative answer only, still sufficient. No need to find exact solution.
PS - Always look at the answers first
CR - Read the question stem first, hunt for conclusion
SC - Meaning first, Grammar second
RC - Mentally connect paragraphs as you proceed. Short = 2min, Long = 3-4 min

Math Expert
Joined: 02 Sep 2009
Posts: 46991
Re: What is the value of the integer n....Exponents [#permalink]

### Show Tags

03 Jan 2013, 03:13
curtis0063 wrote:
Bunuel wrote:
ajit257 wrote:
What is the value of the integer n?

(1) n(n + 2) = 15
(2) (n + 2)^n = 125

What is the value of the integer n?

(1) n(n + 2) = 15 --> $$n^2+2n-15=0$$ --> $$(n+5)(n-3)=0$$ --> $$n=-5$$ or $$n=3$$. Not sufficient.

Dear Bunuel,

My fist approach for statement 1 is 15=3X5, so my reasoning is n(n+2)=3X5. Only n=3 match to that equation, so I pick up D. Could you tell me any thing wrong from my reasoning? THX!

You need to brush up fundamentals.

_________________
Intern
Joined: 28 Jan 2013
Posts: 30
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

04 Sep 2014, 07:10
curtis0063 wrote:
Bunuel wrote:
ajit257 wrote:
What is the value of the integer n?

(1) n(n + 2) = 15
(2) (n + 2)^n = 125

What is the value of the integer n?

(1) n(n + 2) = 15 --> $$n^2+2n-15=0$$ --> $$(n+5)(n-3)=0$$ --> $$n=-5$$ or $$n=3$$. Not sufficient.

Dear Bunuel,

My fist approach for statement 1 is 15=3X5, so my reasoning is n(n+2)=3X5. Only n=3 match to that equation, so I pick up D. Could you tell me any thing wrong from my reasoning? THX!

15 can also be written as -3 * -5... if n= -5 then n(n+2) => -5 * -3= 15
So A cannot provide an unique solution.
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 5825
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

22 Sep 2015, 04:52
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem.
Remember equal number of variables and independent equations ensures a solution.

What is the value of the integer n?

(1) n(n + 2) = 15
(2) (n + 2)^n = 125

In the original condition there is 1 variable (n) and thus we need 1 equation to match the number of variable and equation. Since there is 1 each in 1) and 2), D has high probability of being the answer.
In case of 1), n^2+2n-15=0, (n+5)(n-3)=0 and thus n=-5,3. The answer is not unique, therefore the condition is not sufficient.
In case of 2), n=3, therefore the answer is unique and the condition is sufficient. Therefore the answer is B.

Normally for cases where we need 1 more equation, such as original conditions with 1 variable, or 2 variables and 1 equation, or 3 variables and 2 equations, we have 1 equation each in both 1) and 2). Therefore D has a high chance of being the answer, which is why we attempt to solve the question using 1) and 2) separately. Here, there is 59 % chance that D is the answer, while A or B has 38% chance. There is 3% chance that C or E is the answer for the case. Since D is most likely to be the answer according to DS definition, we solve the question assuming D would be our answer hence using 1) and 2) separately. Obviously there may be cases where the answer is A, B, C or E.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only \$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Manager
Status: IF YOU CAN DREAM IT, YOU CAN DO IT
Joined: 03 Jul 2017
Posts: 211
Location: India
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

14 Jul 2017, 12:20
In statement one: n(n+2)=15 can we say that either n = 15 or n+2=15 n =13. Am i wrong?? Or is this method too correct??
Senior Manager
Joined: 06 Jul 2016
Posts: 417
Location: Singapore
Concentration: Strategy, Finance
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

14 Jul 2017, 12:41
1
longhaul123 wrote:
In statement one: n(n+2)=15 can we say that either n = 15 or n+2=15 n =13. Am i wrong?? Or is this method too correct??

Nope.
if you say that, you're meaning to say that 15*13 = 15 which is not possible.
You can only say that when n(n+2) = 0
i.e. n = 0,-2 <= 2 solutions for the equation.

n^{2} + 2n -15 = 0
n = -5,3

Alternatively
You can plug in values.
n(n+2) = 15
15 = 1*15 or 3*5

n = 3
3*5 =15

But if n = -5
n+2 = -3
-3*(-5) = 15

2 values so the statement is not sufficient.

Hope this helps.
_________________

Put in the work, and that dream score is yours!

Intern
Joined: 08 Jul 2017
Posts: 2
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

29 Nov 2017, 12:44
Also, doesn't the rule says that we can compare exponents only if the bases are same. We cannot assume n+2 and 5 are equal so we need help of statement I to know that n can take 5 as value. Pls correct me if I am wrong
Math Expert
Joined: 02 Sep 2009
Posts: 46991
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

29 Nov 2017, 20:55
narayani20 wrote:
Also, doesn't the rule says that we can compare exponents only if the bases are same. We cannot assume n+2 and 5 are equal so we need help of statement I to know that n can take 5 as value. Pls correct me if I am wrong

n = 5 does not fit. Please check here: https://gmatclub.com/forum/what-is-the- ... ml#p843731
_________________
Senior Manager
Joined: 31 May 2017
Posts: 284
Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

### Show Tags

30 Nov 2017, 22:59
I got the answer B as correct one.

But i plugged in values to find the answer.

What is the value of the integer n?

(1) n(n + 2) = 15
N can be either 3 or -5. We get 2 possible options so Not Sufficient.

(2) (n + 2)^n = 125
N can only be 3. Only one answer. - Sufficient.
_________________

Please give kudos if it helps

Resources
| | | | |

Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n   [#permalink] 30 Nov 2017, 22:59
Display posts from previous: Sort by

# Events & Promotions

 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®.