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# Is n an integer?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 7612
GMAT 1: 760 Q51 V42
GPA: 3.82

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17 Aug 2018, 02:28
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Difficulty:

45% (medium)

Question Stats:

54% (01:15) correct 46% (00:46) wrong based on 58 sessions

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[Math Revolution GMAT math practice question]

Is $$n$$ an integer?

1) $$3n$$ is an integer
2) $$4n$$ is an integer

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
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"Only $79 for 1 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Expert Joined: 02 Aug 2009 Posts: 7764 Re: Is n an integer? [#permalink] ### Show Tags 17 Aug 2018, 02:37 1 [quote="MathRevolution"][Math Revolution GMAT math practice question] Is $$n$$ an integer? 1) $$3n$$ is an integer It is possible if # n is an integer # n is a fraction with just 3 in DENOMINATOR, for example 1/3,2/3 etc Insufficient 2) $$4n$$ is an integer It is possible if # n is an integer # n is a fraction with just 2 or 4 in DENOMINATOR, for example 1/2, 3/4 9/4 etc Insufficient Combined.. Only case left n is an integer Sufficient C _________________ NUS School Moderator Joined: 18 Jul 2018 Posts: 985 Location: India Concentration: Finance, Marketing WE: Engineering (Energy and Utilities) Re: Is n an integer? [#permalink] ### Show Tags 17 Aug 2018, 06:22 chetan2u wrote: MathRevolution wrote: [Math Revolution GMAT math practice question] Is $$n$$ an integer? 1) $$3n$$ is an integer It is possible if # n is an integer # n is a fraction with just 3 in DENOMINATOR, for example 1/3,2/3 etc Insufficient 2) $$4n$$ is an integer It is possible if # n is an integer # n is a fraction with just 2 or 4 in DENOMINATOR, for example 1/2, 3/4 9/4 etc Insufficient Combined.. Only case left n is an integer Sufficient C Hi sir, Correct me if I'm wrong. On combining shouldn't we take the LCM of 3n and 4n which is 12n and n can be 1/12 or 1. Both yes or no is possible. Hence E is the answer? _________________ Press +1 Kudos If my post helps! Math Expert Joined: 02 Aug 2009 Posts: 7764 Is n an integer? [#permalink] ### Show Tags 17 Aug 2018, 06:37 Afc0892 wrote: chetan2u wrote: MathRevolution wrote: [Math Revolution GMAT math practice question] Is $$n$$ an integer? 1) $$3n$$ is an integer It is possible if # n is an integer # n is a fraction with just 3 in DENOMINATOR, for example 1/3,2/3 etc Insufficient 2) $$4n$$ is an integer It is possible if # n is an integer # n is a fraction with just 2 or 4 in DENOMINATOR, for example 1/2, 3/4 9/4 etc Insufficient Combined.. Only case left n is an integer Sufficient C Hi sir, Correct me if I'm wrong. On combining shouldn't we take the LCM of 3n and 4n which is 12n and n can be 1/12 or 1. Both yes or no is possible. Hence E is the answer? No you will take them separately.. if n=1/12, 3n=3*1/12=1/4 which is NOT an integer but 3n is an integer So take 3n and 4n separately _________________ Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 7612 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Is n an integer? [#permalink] ### Show Tags 19 Aug 2018, 18:43 => Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. Condition 1) If $$n = 1$$, the answer is ‘yes’. If $$n = \frac{1}{3}$$, the answer is ‘no’. Since we don’t have a unique solution, condition 1) is not sufficient. Condition 2) If $$n = 1$$, the answer is ‘yes’. If $$n = \frac{1}{4}$$, the answer is ‘no’. Since we don’t have a unique solution, condition 2) is not sufficient. Conditions 1) & 2) Since $$n = 4n – 3n$$ is a difference of two integers, $$n$$ is also an integer. Conditions 1) and 2) are sufficient, when considered together. Therefore, C is the answer. Answer: C If the original condition includes “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations” etc., one more equation is required to answer the question. If each of conditions 1) and 2) provide an additional equation, there is a 59% chance that D is the answer, a 38% chance that A or B is the answer, and a 3% chance that the answer is C or E. Thus, answer D (conditions 1) and 2), when applied separately, are sufficient to answer the question) is most likely, but 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$79 for 1 month Online Course"
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Re: Is n an integer?   [#permalink] 19 Aug 2018, 18:43
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