Is X a multiple and factor of itself

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wilderness
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Posted: Tue Jul 08, 2008 6:27 am Post subject: Is X a multiple and factor of itself

On GMAT when calculating factors and multiple of an integer X, should X be considered a factor and a multiple of itself. Thanks.

Ian Stewart
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Posted: Tue Jul 08, 2008 8:12 am Post subject:

If X is a positive integer, then yes. As an example, if X = 12, the multiples of X are ...-24, -12, 0, 12, 24, ... and the positive divisors of X are 1, 2, 3, 4, 6, and 12.

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wilderness
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Posted: Tue Jul 08, 2008 8:23 am Post subject:

Ian Stewart wrote:

If X is a positive integer, then yes .

Hi Ian,

Thanks for the answer. Regarding the comment about if X is +ve,

1) do we really talk about factors of a -ve number ?

2) If yes, then why does this rule not apply to that case. Afterall just like 2/2 = 1 and -2/-2 = 1 and 2*1=2 and -2*1 = 2.

Thanks in advance.

Ian Stewart
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Posted: Tue Jul 08, 2008 3:02 pm Post subject:

wilderness wrote:

1) do we really talk about factors of a -ve number ?

2) If yes, then why does this rule not apply to that case. Afterall just like 2/2 = 1 and -2/-2 = 1 and 2*1=2 and -2*1 = 2.

Thanks in advance.

Re 1), not in any GMAT question I've ever seen. I've only ever seen GMAT questions that ask about 'positive divisors', and divisibility questions seem to always be restricted to positive integers.

The rules are, as you point out, the same for negatives and positives- when I was restricting things to positives in my first post, I was actually only trying to exclude zero (zero is a bit of an exception- zero is a multiple of itself, but not a divisor of itself- that's not a technicality you need to be concerned about for the GMAT). And, of course, I was limiting the discussion to the case that's relevant on the GMAT.

wilderness
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Posted: Wed Jul 09, 2008 12:37 am Post subject:

Thanks !

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