##### This topic has expert replies
Senior | Next Rank: 100 Posts
Posts: 53
Joined: 02 Jul 2009
Thanked: 2 times

### set P

by clar » Wed Aug 19, 2009 4:30 pm
If P is a set of integers and 3 is in P, are all the positive multiples of 3 in P?

a)If x is in P, then x+3 is in P

b)If x is in P then x-3 is in P

Senior | Next Rank: 100 Posts
Posts: 53
Joined: 02 Jul 2009
Thanked: 2 times
by clar » Wed Aug 19, 2009 4:33 pm
the ans according to me should be A but it is given to be C

Can someone explain how?

my reasoning says that

if 3 is in P and x+3 is also in P , then all positive multiples of 3 will be in P.

this is because for both the above conditions to be valid , the value of x should be 0.

where am i faltering?

Legendary Member
Posts: 752
Joined: 17 May 2009
Location: Tokyo
Thanked: 81 times
GMAT Score:680
by tohellandback » Wed Aug 19, 2009 6:44 pm
clar wrote:the ans according to me should be A but it is given to be C

Can someone explain how?

my reasoning says that

if 3 is in P and x+3 is also in P , then all positive multiples of 3 will be in P.

this is because for both the above conditions to be valid , the value of x should be 0.

where am i faltering?
you are right
because if 3 is there in the set then all the multiples must be there

a) SUFF

b)NOT SUFF, because it will depend upon what the set is
it can be {...-6,-3,0,3}
or it can be the infinite set {...-6,-3,0,3,6.....}
NOT SUFF
The powers of two are bloody impolite!!

Senior | Next Rank: 100 Posts
Posts: 37
Joined: 31 Jul 2009
Thanked: 1 times
by acenikk » Thu Aug 20, 2009 6:25 am
I also go with A.

Master | Next Rank: 500 Posts
Posts: 103
Joined: 04 May 2009
Thanked: 6 times
by navalpike » Thu Aug 20, 2009 8:12 am
Could you please provide the source of the question so that we can avoid it?

Master | Next Rank: 500 Posts
Posts: 157
Joined: 07 Oct 2008
Thanked: 3 times
by PussInBoots » Thu Aug 20, 2009 11:43 am
Definitely A

Senior | Next Rank: 100 Posts
Posts: 36
Joined: 21 Jun 2009
Thanked: 1 times
GMAT Score:700
by iamjakekim » Thu Aug 20, 2009 4:58 pm
Why C?

I got E.

If X were 2, then we would get 5 or -1.
If X were 3, then we would get 6 or 3, hence multiple of 3.

Senior | Next Rank: 100 Posts
Posts: 39
Joined: 03 Jan 2009
by woo » Fri Aug 21, 2009 4:37 am
C is right coz 0 is also a multiple of 3.
In fact, 0 is multiple of every natural number.

• Page 1 of 1