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If x is a positive integer, what is x? (1) x^2 + 7x – 18 = 0 (2) x^2

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Director
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GMAT 1: 670 Q46 V36
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If x is a positive integer, what is x? (1) x^2 + 7x – 18 = 0 (2) x^2  [#permalink]

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New post 05 Apr 2019, 08:20
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Question Stats:

57% (00:55) correct 43% (01:07) wrong based on 54 sessions

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If x is a positive integer, what is x?

(1) x^2 + 7x – 18 = 0

(2) x^2 – 7x + 10 = 0
Director
Director
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Joined: 24 Oct 2016
Posts: 586
GMAT 1: 670 Q46 V36
GMAT 2: 690 Q47 V38
Re: If x is a positive integer, what is x? (1) x^2 + 7x – 18 = 0 (2) x^2  [#permalink]

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New post 05 Apr 2019, 08:22
dabaobao wrote:
If x is a positive integer, what is x?

(1) x^2 + 7x – 18 = 0

(2) x^2 – 7x + 10 = 0



The Crucial Info Trap – The Devil is in the Details

Courtesy: Manhattan Prep (https://gmatclub.com/forum/4-common-typ ... 94680.html)

If the GMAT tells you a piece of information, there’s usually a reason for it. But all too often, students will spend all their time doing the math and completely forget a crucial statement that the GMAT gave.

Besides being a 1 looks like 2 trap, this question has a crucial piece of information hidden at the beginning that leads to a lot of wrong answer choices: x is positive. Statement 1 tells us x could be -9 or 2, but because x must be positive, we know what x must be. Statement 2 tells us x could be 2 or 5, but both of these values are positive. The correct answer is A.

Takeaway


As you read a question, write any important information down on paper so you don’t forget them once you dive into the computations.
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Re: If x is a positive integer, what is x? (1) x^2 + 7x – 18 = 0 (2) x^2  [#permalink]

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New post 05 Apr 2019, 09:47
Top Contributor
dabaobao wrote:
If x is a positive integer, what is x?

(1) x² + 7x – 18 = 0

(2) x² – 7x + 10 = 0


Given: x is a positive integer

Target question: What is the value of x?

Statement 1: x² + 7x – 18 = 0
Factor: (x + 9)(x - 2) = 0
So, EITHER x = -9 OR x = 2
Since we're told x is POSITIVE, we can rule out x = -9
So, the answer to the target question is x = 2
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: x² – 7x + 10 = 0
Factor: (x - 5)(x - 2) = 0
So, EITHER x = 5 OR x = 2
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT


Answer: A

Cheers,
Brent
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Re: If x is a positive integer, what is x? (1) x^2 + 7x – 18 = 0 (2) x^2   [#permalink] 05 Apr 2019, 09:47
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