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The function y=px^2-4x+q in the x-y plane attains a

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 5577
GMAT 1: 800 Q59 V59
GPA: 3.82
The function y=px^2-4x+q in the x-y plane attains a [#permalink]

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Updated on: 09 Jan 2018, 18:53
00:00

Difficulty:

55% (hard)

Question Stats:

49% (00:44) correct 51% (01:04) wrong based on 74 sessions

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[GMAT math practice question]

The function $$y=px^2-4x+q$$ in the $$xy$$-plane attains a minimum value. What is the value of $$x$$?

1) $$p = 2$$
2) $$q = 5$$

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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.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Originally posted by MathRevolution on 08 Jan 2018, 01:26. Last edited by MathRevolution on 09 Jan 2018, 18:53, edited 2 times in total. PS Forum Moderator Joined: 25 Feb 2013 Posts: 1142 Location: India GPA: 3.82 Re: The function y=px^2-4x+q in the x-y plane attains a [#permalink] Show Tags 08 Jan 2018, 01:39 MathRevolution wrote: [GMAT math practice question] The function $$y=px^2-4x+q$$ in the $$x-y$$ plane attains a minimum value. What is the value of $$x$$? 1) $$p = 2$$ 2) $$q = 5$$ Minimum value of a quadratic equation is at $$\frac{-b}{2a}$$ here $$b=-4$$ and $$a=p$$, so minimum $$x=\frac{4}{2p}$$. We need the value of $$p$$ to find the minimum value. Statement 1: $$p=2$$. Sufficient Statement 2: value of $$p$$ is not mentioned. Insufficient Option A Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 5577 GMAT 1: 800 Q59 V59 GPA: 3.82 Re: The function y=px^2-4x+q in the x-y plane attains a [#permalink] Show Tags 10 Jan 2018, 01:00 => 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. $$y=px^2-4x+q$$ has a minimum value when $$x = \frac{-(-4)}{2p} = \frac{2}{p}.$$ Thus, the question asks for the value of $$p$$. Since only condition 1) gives us information about p, only condition 1) is sufficient. Therefore, A is the answer. Answer: A _________________ 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$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Re: The function y=px^2-4x+q in the x-y plane attains a   [#permalink] 10 Jan 2018, 01:00
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