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factor and odd DS questions

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factor and odd DS questions

by charmaine » Sun Sep 14, 2008 7:27 pm
Q1
is 12 a factor of the positive integer n ?
1) n is a factor of 36
2) 3 is a factor of n

Q2
is the integer n odd?
1) n is divisible by 3
2) 2n is divisible by twice as many positive integers as n


[spoiler] 1, ans. E 2, ans. B


thanks you guys[spoiler][/spoiler]
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Re: factor and odd DS questions

by Sunny22uk » Sun Sep 14, 2008 8:16 pm
charmaine wrote:Q1
is 12 a factor of the positive integer n ?
1) n is a factor of 36
2) 3 is a factor of n
q1)
Statement A: n is a factor of 36, that doesnot tell us if 12 is a factor of n, e.g. we can take 2 cases :-
a)n could equal 2(since 2 is a factor of 36), 12 is not a factor of 2, hence is not a factor of n.
b)n could equal 36(since 2 is a factor of 36 as well), in this case 12 is a factor of 36 and hence is a factor of n.
HENCE NOT SUFFICIENT
Statement B 3 is a factor of n,you can use the same reasoning as A
NOT SUFFICIENT
Combining 2 statements we get multiple values for n, some of them are multiples of 12 others are not.
HENCE NOT SUFFICIENT
Answer E
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Re: factor and odd DS questions

by Sunny22uk » Sun Sep 14, 2008 8:29 pm
charmaine wrote: Q2
is the integer n odd?
1) n is divisible by 3
2) 2n is divisible by twice as many positive integers as n
Statement A:- if n is divisble by 3, n can be odd or even(e.g. 3,6)
Not sufficient
Statement A:- lets suppose n=2, 2n=4
2 is divisible by 1 and 2, 4 is divisible by 1,2,4
2n does not have twice as many divisors as n (if n is even)
Also , lets say n=3, 2n=6, 2n is divisible by 1,2,3,6
3 is divisible by 1 and 3, 6 is divisible by 1,2,3,6
If n is even, 2n will have twice as many divisors as n(if n is odd).
Thus N is odd
Answer is B
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by Sunny22uk » Sun Sep 14, 2008 8:31 pm
Thanks for posting the answer in spoilers. :D
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by charmaine » Sun Sep 14, 2008 8:47 pm
i will alwiz try to accomodate the wishes of my lil helpers :)
cheers
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by niraj_a » Mon Sep 15, 2008 8:59 am
charmaine, are these from GPrep?
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by Brent@GMATPrepNow » Mon Oct 21, 2019 8:54 am
charmaine wrote:Q1
is 12 a factor of the positive integer n ?
1) n is a factor of 36
2) 3 is a factor of n
Target question: Is 12 a factor of the positive integer n?

Statement 1: n is a factor of 36
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of n that satisfy statement 1. Here are two:
Case a: n = 12, in which case 12 IS a factor of n
Case b: n = 6, in which case 12 is NOT a factor of n
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: 3 is a factor of n
Once again, there are several values of n that satisfy statement 2. Here are two:
Case a: n = 12, in which case 12 IS a factor of n
Case b: n = 6, in which case 12 is NOT a factor of n
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
IMPORTANT: Notice that I was able to use the same counter-examples to show that each statement ALONE is not sufficient. So, the same counter-examples will satisfy the two statements COMBINED.
In other words,
Case a: n = 12, in which case 12 IS a factor of n
Case b: n = 6, in which case 12 is NOT a factor of n
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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