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What is the remainder when the positive integer x is divided

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RonPurewal
 Post subject: Re: What is the remainder when the positive integer x is divided
 Post Posted: Fri Jun 24, 2011 6:21 am 
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ManhattanGMAT Staff


Posts: 7146
jeevan13 wrote:
Hey Ron,

I understand it is easy to do these kind of questions by just substituting a number. But it would be really nice if you could explain to me the method for:


i really don't know -- maybe i'm just really tired today, but i honestly can't follow the proof/argument above.
however, i can really, truly, honestly tell you that any piece of number-theory argumentation that is this long and convoluted ... is not going to help you on test day. quite the opposite, actually.

the purpose of many problems on this test is to be outrageously difficult, or even impossible, to solve by “textbook” methods.
the POINT of these problems is the mental flexibility -- i.e., the problem is not so much intended to test remainders as it's intended to test your ability to quit using approaches that aren't working and start using backup approaches.
by continuing to hammer your head against the proverbial brick wall, you are totally walking right into the trap that the test makers are setting for you.

for a whole hour and a half of problems on which traditional algebra doesn't work at all, see the NOVEMBER 4 lecture at the following address:
http://www.manhattangmat.com/thursdays-with-ron.cfm
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rachelhong2012
 Post subject: Re: What is the remainder when the positive integer x is divided
 Post Posted: Sun Jan 15, 2012 1:51 pm 
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Course Students


Posts: 47
Hi,

I know we can plug #'s to test the choices. But I wonder if this theoretical approach is also correct:

What is the remainder when positive integer x is divided by 3?

Looking at the question, I generated 3 possibilities:

multiple of 3 + remainder of 0
multiple of 3 + remainder of 1
multiple of 3 + remainder of 2
The rephrased question: which possiblity is it?

a. When x is divided by 6 remainder is 2

x = multiple of 6 + remainder of 2
x = multiple of 3 + remainder of 2

sufficient
b. When x is divided by 15, remainder is 2

x = multiple of 15 + remainder of 2
x = multiple of 3 + remainder of 2

sufficient


Am I right?
Thanks!
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tim
 Post subject: Re: What is the remainder when the positive integer x is divided
 Post Posted: Sun Jan 15, 2012 4:25 pm 
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ManhattanGMAT Staff


Posts: 2242
Location: Southwest Airlines, seat 21C
yes, but this only works because 3 is a factor of both 6 and 15..

_________________
Tim Sanders
Manhattan GMAT Instructor
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rachelhong2012
 Post subject: Re: What is the remainder when the positive integer x is divided
 Post Posted: Sun Jan 15, 2012 7:40 pm 
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Course Students


Posts: 47
tim wrote:
yes, but this only works because 3 is a factor of both 6 and 15..


I see, thanks Tim!
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tim
 Post subject: Re: What is the remainder when the positive integer x is divided
 Post Posted: Sun Jan 15, 2012 11:24 pm 
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ManhattanGMAT Staff


Posts: 2242
Location: Southwest Airlines, seat 21C
no problem!

_________________
Tim Sanders
Manhattan GMAT Instructor
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