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 Post subject: Inequalities Quadratic equation
PostPosted: Wed Dec 30, 2009 6:18 am 
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Joined: Tue Dec 28, 2004 2:34 am
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Which of the following is correct if x is a real number and (x - 11)(x - 3) is negative?
A. x^2 + 5x + 6 < 0
B. x^2 + 5x + 6 > 0
C. 5 - x < 0
D. x - 5 < 0
E. 11 - x > 0

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 Post subject: Re: Inequalities Quadratic equation
PostPosted: Wed Dec 30, 2009 6:39 am 
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Joined: Wed Nov 04, 2009 5:50 am
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(x-11)(x-3) will be negative when 3<x<11 and;
x^2+5x+6=(x+2)(x+3) and this equation is negative when -3<x<-2 and will be positive when x>-2 or either x<-3
As a result I think none of these choices can be true in this special case, because regarding to the above situations if you check, it can be seen that none of these answers is true!!!


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 Post subject: Re: Inequalities Quadratic equation
PostPosted: Wed Dec 30, 2009 9:28 am 
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You are right about the solution set. However, you inferred it incorrectly.

As you had said when (x - 11)(x - 3) < 0, 3 < x < 11.

Choice B results in a solution set x > -2 or x < -3.

So, a value of x between 3 and 11 will certainly satisfy the condition that x^2 + 5x + 6 > 0.

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 Post subject: Re: Inequalities Quadratic equation
PostPosted: Wed Dec 30, 2009 5:11 pm 
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Joined: Wed Nov 04, 2009 5:50 am
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Yes, you are right, but as you resulted in the selection of choice (B), also we can say that the choice (E), because when 3<x<11 then it can satisfy choice (E) which is 11-x>0. Am I right? I just followed your logic resulted in the (B) selection and with similar logic choice (E) can be true also!


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 Post subject: Re: Inequalities Quadratic equation
PostPosted: Thu Jan 07, 2010 3:39 am 
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Joined: Tue Dec 28, 2004 2:34 am
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You are absolutely right.

Error regretted. Both B and E are correct answers.

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ACE GMAT Quant with 4GMAT's Advanced Math Lesson Books, eBooks.
Next Weekend Batch @ Chennai starts Feb 18, 2012


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