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akshaydhande
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Kiindy help with is DS problem
This topic has expert replies
Source: Beat The GMAT — Data Sufficiency |
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akshaydhande
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Brent@GMATPrepNow
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Here's one solution (in case others are having difficulty)
Here's the full question and one possible solution.
This question is a great candidate for rephrasing the target question.
Aside: We have a video with tips on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100
To begin, notice that we have two nice rules:
- If k > 0, then √(k²) = k
- If k < 0, then √(k²) = -k
Now observe that (3-x) = -(x-3)
Given the above information, under what conditions will √[(x-3)²] = 3-x?
In other words, under what conditions will √[(x-3)²] = -(x-3)?
This will occur IF x-3 is NEGATIVE.
So, we can now rephrase the target question as: Is (x-3) negative?
Or we can write: Is x-3 < 0?
Or better yet...
REPHRASED target question: Is x < 3?
Now that we've REPHRASED the target question in much simpler terms, we can check the statements.
Statement 1: x not equal to 3
This does not give us a definitive answer to the REPHRASED target question (Is x < 3? )
As such, statement 1 is NOT SUFFICIENT
Statement 2: -x|x| > 0
First notice that this implies that x does not equal zero.
Next, notice that, if x does not equal zero, then |x| will always be positive.
So, -x|x| > 0 is the same as saying (-x)(positive) > 0
In other words, the product (-x)(positive) results in a positive number.
This tells us that (-x) must be positive, which means x must be negative.
If x is negative, then x is definitely less than 3.
Since we can answer the REPHRASED target question with certainty, statement 2 is SUFFICIENT
Answer = B
Cheers,
Brent
Here's the full question and one possible solution.
Target question: Is √[(x - 3)²] = 3 - x ?Is √[(x - 3)²] = 3 - x ?
1. x is not equal to 3
2. -x|x| > 0
This question is a great candidate for rephrasing the target question.
Aside: We have a video with tips on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100
To begin, notice that we have two nice rules:
- If k > 0, then √(k²) = k
- If k < 0, then √(k²) = -k
Now observe that (3-x) = -(x-3)
Given the above information, under what conditions will √[(x-3)²] = 3-x?
In other words, under what conditions will √[(x-3)²] = -(x-3)?
This will occur IF x-3 is NEGATIVE.
So, we can now rephrase the target question as: Is (x-3) negative?
Or we can write: Is x-3 < 0?
Or better yet...
REPHRASED target question: Is x < 3?
Now that we've REPHRASED the target question in much simpler terms, we can check the statements.
Statement 1: x not equal to 3
This does not give us a definitive answer to the REPHRASED target question (Is x < 3? )
As such, statement 1 is NOT SUFFICIENT
Statement 2: -x|x| > 0
First notice that this implies that x does not equal zero.
Next, notice that, if x does not equal zero, then |x| will always be positive.
So, -x|x| > 0 is the same as saying (-x)(positive) > 0
In other words, the product (-x)(positive) results in a positive number.
This tells us that (-x) must be positive, which means x must be negative.
If x is negative, then x is definitely less than 3.
Since we can answer the REPHRASED target question with certainty, statement 2 is SUFFICIENT
Answer = B
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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DavidG@VeritasPrep
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And the GMAT loves including absolute values in inequality questions. See here for another one: https://www.beatthegmat.com/is-x-1-gmat- ... 65922.html
