BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

DATA SUFFICIENCY SET

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 124
Joined: Sun Mar 07, 2010 3:15 pm
Thanked: 1 times

DATA SUFFICIENCY SET

by francoisph » Tue Jun 01, 2010 5:53 am
Hi,

Please someone could explain me?

S is a set of positive integers such that if integer x is a member of S, the both x^2 and x^3 are also
in S. If the the only member of S that is neither the square nor the cube of another member of S is called the source integer, is 8 in S?

1° 4 is in S and is not the source integer

2° 64 is in S and is not the source integer

thks
Top
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 106
Joined: Mon Sep 28, 2009 9:29 am
Location: Boston, MA
Thanked: 26 times
Followed by:2 members
GMAT Score:700

by asamaverick » Tue Jun 01, 2010 6:22 am
1) 4 is in S and not a source integer. If a number is a source integer then its square and cube should be present in S, but the number itself need not be square or cube of another number. Since 4 is not a source integer, we can interpret that 2 is also present in S. 4 is in the set since it a square of 2. If 2 is present in S, then the cube of 2 (8) should also be present. Hence (1) is sufficient.

2) 64 is in S and not a source integer. Since 64 is not a source integer, it can be in the set as a square (of 8) or as a cube (of 4). If it is present in the set as a cube of 4 (and we do not know just by (2) alone if 4 is a source number or not) we cannot say if 8 is present in S. Hence (2) alone is not sufficient.

So think the answer should be A. What is the OA?
Top
Legendary Member
Posts: 2326
Joined: Mon Jul 28, 2008 3:54 am
Thanked: 173 times
Followed by:2 members
GMAT Score:710

by gmatmachoman » Tue Jun 01, 2010 7:48 am
asamaverick wrote:1) 4 is in S and not a source integer. If a number is a source integer then its square and cube should be present in S, but the number itself need not be square or cube of another number. Since 4 is not a source integer, we can interpret that 2 is also present in S. 4 is in the set since it a square of 2. If 2 is present in S, then the cube of 2 (8) should also be present. Hence (1) is sufficient.

2) 64 is in S and not a source integer. Since 64 is not a source integer, it can be in the set as a square (of 8) or as a cube (of 4). If it is present in the set as a cube of 4 (and we do not know just by (2) alone if 4 is a source number or not) we cannot say if 8 is present in S. Hence (2) alone is not sufficient.

So think the answer should be A. What is the OA?
sT 2 IS REALLY TRICKY.
AS rightly said, 64 is in the set. Now it's prescence is becox of 8 or 4 is a mystery.

Case 1 : 64 is in S. so is 8

YES

case 2: 64 is in S. So is 4.

What if 4 is Not source integer: The set will contain 2 & thereby 8/

But what if 4 is source integer :? 2 wont be there in set. So No 2 & No 8

In consistent. Insufficient!

Pick A
Top
Master | Next Rank: 500 Posts
Posts: 124
Joined: Sun Mar 07, 2010 3:15 pm
Thanked: 1 times

by francoisph » Wed Jun 02, 2010 6:09 am
kaplan said

1 sufficient

2 sufficient
Top
Legendary Member
Posts: 2326
Joined: Mon Jul 28, 2008 3:54 am
Thanked: 173 times
Followed by:2 members
GMAT Score:710

by gmatmachoman » Wed Jun 02, 2010 9:50 am
francoisph wrote:kaplan said

1 sufficient

2 sufficient
Can u post the explanation of how St 2 is sufficient??
Top
Master | Next Rank: 500 Posts
Posts: 124
Joined: Sun Mar 07, 2010 3:15 pm
Thanked: 1 times

by francoisph » Wed Jun 02, 2010 11:57 am
Statement (1): Sufficient
If 4 is in S, and it is not the source integer, then it must be the square
or cube of the source integer. Since 4 is not the cube of any positive
integer, and it is the square of 2, 2 must be in S and must be the source
integer. It follows that if 2 is the source integer, 4 is the square of 2,
and 8 is the cube of 2. So 2, 4, and 8 would be in S. Statement (1) by
itself is sufficient to answer the question.

Statement (2): Sufficient
If 64 is in S and it is not the source integer, it could represent the
square of 8 or the cube of 4. If it represents the square of 8, then 8, 64,
and 512 are in S. The number 8 would be a member of S in this case as well.

If 64 represents the cube of 4, then 4, 16, and 64 would be in S. Since 4
is the square of 2, 2 would be in S, and 8 (the cube of 2) would also be in
S.

Either statement by itself is sufficient to answer the question.
Top
Master | Next Rank: 500 Posts
Posts: 124
Joined: Sun Mar 07, 2010 3:15 pm
Thanked: 1 times

by francoisph » Thu Jun 03, 2010 12:10 pm
KAPLAN S MISTAKE

it should be 1) sufficiency
Top
Post new topic Post Reply
• Page 1 of 1