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GMAT Prep - Number properties

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Re: GMAT Prep - Number properties

by Neo2000 » Mon Sep 03, 2007 8:19 pm
tutonaranjo wrote:Is the integer n a multiple of 15?

1) n is a multiple of 20

2) n + 6 is a multiple of 3

Answer is C. Appreciatte a detailed explanation.
To be divisible by 15 it must have factors 3 and 5

From 1 we know that n i divisble by 20 so it could be 20,40,80 or maybe 60
Thus n has factors 5 and 4 for sure and probably 3 but not known

From 2 we know that is divisble by 3 since (n+6)/3 = n/3 +6/3 and this is still a multiple
So n has a factor 3 for sure but we dont know if it has 5 as a factor.

Combining both, we get that n has factors 3, 4 and 5 thus ensuring that it is a multiple of 15
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Re: GMAT Prep - Number properties

by jaspreet.sharma » Mon Sep 03, 2007 9:39 pm
Neo2000 wrote:
tutonaranjo wrote:Is the integer n a multiple of 15?

1) n is a multiple of 20

2) n + 6 is a multiple of 3

Answer is C. Appreciatte a detailed explanation.
To be divisible by 15 it must have factors 3 and 5

From 1 we know that n i divisble by 20 so it could be 20,40,80 or maybe 60
Thus n has factors 5 and 4 for sure and probably 3 but not known

From 2 we know that is divisble by 3 since (n+6)/3 = n/3 +6/3 and this is still a multiple
So n has a factor 3 for sure but we dont know if it has 5 as a factor.

Combining both, we get that n has factors 3, 4 and 5 thus ensuring that it is a multiple of 15



1st stmt -> 20,40,60......

2nd stmt -> n+6 is a multiple of 3 -> n is a multiple of 3
for n = 54
n+6 = 60 (which is a multiple of 20 n 15 too)

This implies C is the answer.

I hope it explained the soln. :)
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by sumithshah » Sun Aug 24, 2008 7:12 am
Keep Neo's method of solving in mind - it'll help on tons of other DS problems

( I'm not implying the other solutions are bad - just that Neo's solution is easily applicable to other problems )
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by andes1 » Sun Aug 24, 2008 9:05 am
What is the number??
LEARNING ENGLIS H
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by pepeprepa » Sun Aug 24, 2008 9:25 am
There is not only one answer.
We just need to know that n is a multiple (or not) of 15 to answer the question.
It could be 0 or 60 or 120 or ...
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by aj5105 » Mon May 04, 2009 1:46 am
(C)
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