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If m is a positive odd integer between 2 and 30, then m is [#permalink]
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23 Jul 2008, 19:37
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This topic is locked. If you want to discuss this question please repost it in the respective forum. If m is a positive odd integer between 2 and 30, then m is divisible by how many different positive prime numbers? (1) m is not divisible by 3. (2) m is not divisible by 5.
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Re: GmatPrep.DS2 [#permalink]
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23 Jul 2008, 19:58
List down all the positive odd numbers b/w 2 and 30: 3,5,7,9,11,13,15,17,19,21,23,25,27,29
S1. 3,9,15,21,27 are out from the list This leaves only 25 which can be divided by 5  hence one prime number only
S2 leaves 3,9,21,27 3 can be divided by 3 only 9 can be divided by 3 only 21 can be divided by 3 and 7 27 can be divided by 3 only Hence maybe case
IMO A
Last edited by x97agarwal on 24 Jul 2008, 18:00, edited 1 time in total.



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Re: GmatPrep.DS2 [#permalink]
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23 Jul 2008, 21:54
my approach, list all possible numbers
3,5,7,9,11,13,15,17,19,21,23,25,27,29
only 15 (3*5) and 21( 3*7) are multiple of two different prime numbers...
statement 1 : can eliminate both 15 and 21  Suff statement 2 : can only eliminate 15, 21 stays  not suff



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Re: GmatPrep.DS2 [#permalink]
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23 Jul 2008, 22:21
GMBA85 wrote: durgesh79 wrote: my approach, list all possible numbers
3,5,7,9,11,13,15,17,19,21,23,25,27,29
only 15 (3*5) and 21( 3*7) are multiple of two different prime numbers...
statement 1 : can eliminate both 15 and 21  Suff statement 2 : can only eliminate 15, 21 stays  not suff How about 25? Which is 5*5. Its "different" prime numbers .... 5 and 5 are same prime numbers



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Re: GmatPrep.DS2 [#permalink]
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24 Jul 2008, 01:58
(1) tells us m can be 5, 7, 11, 13, 15, 17, 19, 23, 25, 29 not sufficient
(2) tells us m can be 3, 7, 9, 11, 13, 17, 19, 21, 23, 27, 29 not sufficient
(1) + (2) tells us m can be 7, 11, 13, 17, 19, 23, 29 sufficient
Answer is (C)
After working with this timeconsuming method, I believe that there is a shortcut.
Is it a rule that between 2 and 30, if the number is not a multiple of 3 or 5, it is a prime number?



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Re: GmatPrep.DS2 [#permalink]
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24 Jul 2008, 03:50
A for me . After eliminating from the list all multiples of 3, the leftover numbers can only be divided by one unique prime number.
From B, after eliminating all relevant #s from the list, you still have 21, which is divisiable by two primes, and numbers like 3, which is divisible by only one prime



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Re: GmatPrep.DS2 [#permalink]
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26 Jul 2008, 19:56
OA is A friends, thanks. I have just come back after relax. Easy one right?
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Re: GmatPrep.DS2 [#permalink]
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27 Jul 2008, 20:45
sondenso wrote: If m is a positive odd integer between 2 and 30, then m is divisible by how many different positive prime numbers?
(1) m is not divisible by 3.
(2) m is not divisible by 5. from 1: 5x7 = 35, which is out of the range. so only one prime divides m. suff.. from 2: any odd prime in the range or 21 (3x7). so either 1 or 2 primes divide(s) m. nsf. A.
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