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The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive inte

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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 ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive inte  [#permalink]

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29 Jun 2016, 19:23
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The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive integers. If the average (arithmetic mean) of them is 18, what is the value of a?
A. 3
B. 6
C. 9
D. 12
E. 15

*An answer will be posted in 2 days.

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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" Intern Joined: 30 Apr 2016 Posts: 8 Re: The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive inte [#permalink] Show Tags 29 Jun 2016, 20:34 (2+3+4)x =18*3 x=6 =>a=2x=2*6=12 Sent from my HTC Desire 816G dual sim using GMAT Club Forum mobile app Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 9006 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive inte [#permalink] Show Tags 03 Jul 2016, 04:42 a=2k, b=3k, c=4k, a+b+c=2k+3k+4k=(18)(3), 9k=18(3), k=6. Therefore, a=2k=2(6)=12, and the correct answer is D. _________________ 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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Joined: 20 Jan 2016
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GMAT 1: 600 Q47 V26
Re: The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive inte  [#permalink]

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03 Jul 2016, 05:02
D. 12
simply 3x will be the AM

X=6
a=2x=12

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Re: The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive inte  [#permalink]

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03 Jul 2016, 05:52
MathRevolution wrote:
The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive integers. If the average (arithmetic mean) of them is 18, what is the value of a?
A. 3
B. 6
C. 9
D. 12
E. 15

*An answer will be posted in 2 days.

Plugging in Answer Choice worked for me

Here given a:b:c=2:3:4 ,So a:b:c=1:$$\frac{3}{2}$$:2

Now by putting value of a=12 on the ratio we can find that only answer choice D matched with a:b:c=12:18:24 ,arithmetic mean of them is $$\frac{12+18+24}{3}$$=18

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Joined: 25 Jun 2016
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Re: The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive inte  [#permalink]

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03 Jul 2016, 06:33
If a list of numbers is 'evenly spaced out,' then the average equals the median. (e.g. in the list {7, 14, 21, 28, 25}, 21 is immediately apparent as the average because each term is separated from the preceding term by the same number)

In this question, a, b and c are evenly spaced out, so we know that b is the average. Therefore b's real value is 18. this means our multiplier is 6. So a is 2*6=12.
Re: The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive inte   [#permalink] 03 Jul 2016, 06:33