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]
factor and odd DS questions
This topic has expert replies
-
- Master | Next Rank: 500 Posts
- Posts: 144
- Joined: Thu Apr 17, 2008 3:33 pm
- Thanked: 8 times
q1)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
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
You cannot discover new oceans unless you have the courage to loose sight of the shore.
-
- Master | Next Rank: 500 Posts
- Posts: 144
- Joined: Thu Apr 17, 2008 3:33 pm
- Thanked: 8 times
Statement A:- if n is divisble by 3, n can be odd or even(e.g. 3,6)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
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
You cannot discover new oceans unless you have the courage to loose sight of the shore.
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Target question: Is 12 a factor of the positive integer n?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
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