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# The cost, c and the revenue, r are related via the equation

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 4904
GPA: 3.82
The cost, c and the revenue, r are related via the equation [#permalink]

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11 Jan 2018, 00:42
00:00

Difficulty:

55% (hard)

Question Stats:

54% (01:11) correct 46% (01:17) wrong based on 56 sessions

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[GMAT math practice question]

The cost, c and the revenue, r are related via the equation c =ar+b. By how much is the cost increased if the revenue is increased by $10? 1) a=0.5 2) b=5 [Reveal] Spoiler: OA _________________ 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. Find a 10% off coupon code for GMAT Club members. “Receive 5 Math Questions & Solutions Daily” Unlimited Access to over 120 free video lessons - try it yourself See our Youtube demo Math Expert Joined: 02 Aug 2009 Posts: 5660 Re: The cost, c and the revenue, r are related via the equation [#permalink] ### Show Tags 11 Jan 2018, 03:40 1 This post received KUDOS Expert's post MathRevolution wrote: [GMAT math practice question] The cost, c and the revenue, r are related via the equation c =ar+b. By how much is the cost increased if the revenue is increased by$10?

1) a=0.5
2) b=5

C=ar+b...
If revenue increases by 10..
$$c_1=a(r+10)+b= ar+10a+b$$..
Increase is 10a, so u require value of only a..
Statement I gives value of a..
Increase=10*0.5=5
Suff

A
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Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 4904
GPA: 3.82
Re: The cost, c and the revenue, r are related via the equation [#permalink]

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14 Jan 2018, 17:26
=>
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.

The equation c = ar + b tells us that the cost is increases by $a when the revenue is increases by$1.
It follows that the cost is increases by $10a when the revenue is increases by$10. So, the question is asking for the value of a.

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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.
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Unlimited Access to over 120 free video lessons - try it yourself

Re: The cost, c and the revenue, r are related via the equation   [#permalink] 14 Jan 2018, 17:26
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