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# The lengths of two sides of a certain triangle are 3 and 9. What is th

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
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GMAT 1: 760 Q51 V42
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The lengths of two sides of a certain triangle are 3 and 9. What is th  [#permalink]

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19 Feb 2018, 01:25
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Difficulty:

25% (medium)

Question Stats:

74% (00:51) correct 26% (00:50) wrong based on 112 sessions

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[GMAT math practice question]

The lengths of two sides of a certain triangle are 3 and 9. What is the length of the 3rd side of the triangle?

1) The perimeter of the triangle is 20
2) The length of the 3rd side of the triangle is a multiple of 4

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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" Senior Manager Joined: 07 Jul 2012 Posts: 371 Location: India Concentration: Finance, Accounting GPA: 3.5 Re: The lengths of two sides of a certain triangle are 3 and 9. What is th [#permalink] ### Show Tags 19 Feb 2018, 02:25 2 Let the third side of triangle= x Statement 1: 3+9+x=20; x=8 [Suff] Statement 2: x is a multiple of 4 Note: a) The length of any side of a triangle must be larger than the positive difference of the other two sides. So x must be greater than (9-3)= 6 b) The length of any side of a triangle must be smaller than the sum of the other two sides. So x must be smaller than (9+3)= 12 8 is the only multiple of 4 which is greater than 6 but smaller than 12. [Suff] Answer: D. _________________ Kindly hit kudos if my post helps! CEO Joined: 12 Sep 2015 Posts: 3966 Location: Canada The lengths of two sides of a certain triangle are 3 and 9. What is th [#permalink] ### Show Tags Updated on: 28 Apr 2018, 10:01 1 Top Contributor MathRevolution wrote: [GMAT math practice question] The lengths of two sides of a certain triangle are 3 and 9. What is the length of the 3rd side of the triangle? 1) The perimeter of the triangle is 20 2) The length of the 3rd side of the triangle is a multiple of 4 Target question: What is the length of the 3rd side of the triangle? Given: The other two sides have lengths 3 and 9 Statement 1: The perimeter of the triangle is 20 Let x = the length of the third side If the perimeter is 20, we can write: 3 + 9 + x = 20 Solve to get: x = 8 So, the answer to the target question is 8 Since we can answer the target question with certainty, statement 1 is SUFFICIENT Statement 2: The length of the 3rd side of the triangle is a multiple of 4 IMPORTANT RULE: If two sides of a triangle have lengths A and B, then . . . DIFFERENCE between A and B < length of third side < SUM of A and B Let x = the length of the third side So, we can write: 9 - 3 < x < 9 + 3 Simplify: 6 < x < 12 Since 8 is the only multiple of 4 between 6 and 12, we can conclude that x = 8 Since we can answer the target question with certainty, statement 2 is SUFFICIENT Answer: D RELATED VIDEO _________________ Test confidently with gmatprepnow.com Originally posted by GMATPrepNow on 19 Feb 2018, 13:32. Last edited by GMATPrepNow on 28 Apr 2018, 10:01, edited 1 time in total. Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 7896 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: The lengths of two sides of a certain triangle are 3 and 9. What is th [#permalink] ### Show Tags 21 Feb 2018, 01:02 => 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. The first step of the VA (Variable Approach) method is to modify the original condition and the question, and then recheck the question. Assume $$x$$ is the length of the 3rd side of the triangle. Since we have 1 variable ($$x$$) and 0 equations, D is most likely to be the answer. So, we should consider each of the conditions on their own first. Note: Since (using the triangle inequality) $$x > 9 + 3 = 12$$ and $$x < 9 – 3 = 6$$, we have $$6 < x < 12.$$ Condition 1) $$x + 3 + 9 = 20$$ Thus $$x = 8$$. Condition 1) is sufficient. Condition 2) The only integer between $$6$$ and $$12$$ that is a multiple of $$4$$ is $$8.$$ Thus, $$x = 8$$. Condition 2) is sufficient, too. In addition, since conditions 1) and 2) are similar, D is most likely to be the answer. Therefore, D is the answer. Answer: D 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: The lengths of two sides of a certain triangle are 3 and 9. What is th   [#permalink] 21 Feb 2018, 01:02
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