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# If |ab|≠ab,Is a>b?

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Manager
Joined: 15 Dec 2015
Posts: 120
GMAT 1: 660 Q46 V35
GPA: 4
WE: Information Technology (Computer Software)

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03 Aug 2017, 09:26
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Difficulty:

45% (medium)

Question Stats:

66% (01:23) correct 34% (01:49) wrong based on 97 sessions

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If |ab|≠ab,Is a>b?

Statement 1: $$|a|>b^3$$
Statement 2: $$a^2<b$$
Manager
Joined: 02 Nov 2015
Posts: 169
GMAT 1: 640 Q49 V29

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03 Aug 2017, 09:50
Statement 1 gives a yes and a No.
Insufficient.
Statement 2 says that B is positive and B>A
Thus sufficient.

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Intern
Joined: 31 Mar 2017
Posts: 2

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27 Jun 2018, 12:22
Given:
|ab|≠ab:
|ab|=ab if ab>=0 --> Not possible
|ab|=-(ab) if ab<0 --> a and b have different signs
Two cases: a>b OR a<b

1) |a|>b^3 --> Something positive > b^3
a>0>b: |+1|>(-1)^3 Holds true. Answer: Yes
a<0<b: |-1|>1^3 Holds true. Answer: No
Two cases with two different answers.

2) a^2<b --> Something positive > b
Per stim:
If a>0 then b<0 --> (+1)^2<-2 Impossible. (2) doesn’t hold true.
If a<0 then b>0 --> (-1)^2<+2 True.
Manager
Joined: 07 Feb 2017
Posts: 171

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27 Jun 2018, 12:27
a<0 or b<0

Statement 1: a=1; b=-1
a=-2; b=1

Statement 2: a^2>0; thus b>0; thus b>a
Sufficient

Manhattan Prep Instructor
Joined: 04 Dec 2015
Posts: 589
GMAT 1: 790 Q51 V49
GRE 1: Q170 V170

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27 Jun 2018, 13:24
1
DHAR wrote:
If |ab|≠ab,Is a>b?

Statement 1: $$|a|>b^3$$
Statement 2: $$a^2<b$$

The question itself contains some extra info. That info is:

|ab|≠ab

Think through what that info actually means. The only situation where a number isn't equal to its own absolute value, is where that number is negative. So, this really just says 'ab is negative'. And if the product of two numbers is negative, exactly one of those numbers is negative. You know for sure that either a is negative, or b is negative, but not both.

You want to know whether a is greater than b. Since one of them is definitely negative and the other is definitely positive, the positive one will definitely always be bigger. Really, all you need to figure out is whether a is the positive number or not.

Statement 1: This doesn't tell you for sure whether a is positive and b is negative, or whether it's the other way around. It can actually go either way. If a = -100 and b = 1, then $$|a|>b^3$$. If a = 100 and b = -1, then $$|a|>b^3$$. So, we don't know for sure which one is the positive number, so it's insufficient.

Statement 2: This does tell you that b has to be positive. $$a^2$$ is a perfect square, which means it can't be any smaller than 0. A perfect square will never be negative. So, it can't be smaller than a negative number! That tells you that b is definitely positive. And since we already know that one of the numbers is positive and the other is negative, we know that a is negative.

Knowing that a is negative and b is positive is enough info to answer the question: a is definitely not greater. So, statement 2 is sufficient.
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Chelsey Cooley | Manhattan Prep Instructor | Seattle and Online

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Re: If |ab|≠ab,Is a>b? &nbs [#permalink] 27 Jun 2018, 13:24
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