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x^2 - y^2 divisible by 8?

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by hardikm » Wed Jun 01, 2011 11:27 am
Hi All,

This question is pretty straightforward according to me. However, I disagree with [spoiler]OA:C[/spoiler]. Please provide your reasoning and answer.

Is x^2 - y^2 divisible by 8?
1. x and y are even integers
2. x + y is divisible by 8

[spoiler]Explanation In solution: Statement 2 is insufficient. the answer to the question is no if x = 7.75 and y =0.25 (x and y are not necessarily integers) I disagree because x^2 - y^2 = (x + y) ( x -y) . [/spoiler]

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by hardikm » Wed Jun 01, 2011 11:29 am
Aaaaargggg... I see it.. I guess the definition of divisibility means no remainder. (x + y) (x -y)
if x = 7.12 y = 0.88 not gonna have 0 remainder..

Trap Question :)
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by SoCan » Wed Jun 01, 2011 12:15 pm
hardikm wrote: Trap Question :)
Yep, that dangerous assumption that the numbers are integers rears its head again. GMatClub seems to really hammer on that one. It's a good thing, because it's really easy to overlook that when you're trying to solve a question quickly, no matter how good you are at math.
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by cans » Wed Jun 01, 2011 3:48 pm
nice question
even i got B initially..
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by pemdas » Fri Jun 03, 2011 2:20 pm
excellent problem which demonstrates how GMAT is testing our brain processing
Our Math wiz and knowledge acts like CEO of big firm and ability to read, recognize the letters, figures and those printed symbols by processing them into data stream to our brain (CEO) is recognized after all Employees (nerves, neural cells, our habitual affections, etc.).

This is where our brain is being tested bottom-up (Employees) versus top-down (CEO). The stuff always happens like this on GMAT. In life we can be assuredly smart if our Employees are smart and we passed through all knowledge tests. BUT on GMAT our Employees may be either dull (stressed-out, blockaded) or we can hasten our Employees (neural cell, eyes, attention) towards reporting to CEO.

we got to be careful on exam, as this is really the test of our brain processing abilities
hardikm wrote:Hi All,

This question is pretty straightforward according to me. However, I disagree with [spoiler]OA:C[/spoiler]. Please provide your reasoning and answer.

Is x^2 - y^2 divisible by 8?
1. x and y are even integers
2. x + y is divisible by 8

[spoiler]Explanation In solution: Statement 2 is insufficient. the answer to the question is no if x = 7.75 and y =0.25 (x and y are not necessarily integers) I disagree because x^2 - y^2 = (x + y) ( x -y) . [/spoiler]

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by baladon99 » Fri Jun 03, 2011 11:13 pm
guess the OA C is correct.
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