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 Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

(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.

Re: What is the value of the integer n....Exponents [#permalink]

Show Tags

01 Jan 2011, 07:12

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.

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.
_________________

Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

Show Tags

04 Jan 2012, 13:14

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

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

Answer: B.

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!

Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

Show Tags

04 Sep 2014, 06:10

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.

Answer: B.

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.

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.
_________________

Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

Show Tags

14 Jul 2017, 11:41

1

This post received KUDOS

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

Re: What is the value of the integer n? (1) n(n + 2) = 15 (2) (n [#permalink]

Show Tags

29 Nov 2017, 11:44

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

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