Is 5 a factor of N?

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valleeny: Senior | Next Rank: 100 Posts; Posts: 59; Joined: Mon Nov 16, 2009 4:54 pmFollowed by: 1 member; Thanked: 8 times

by valleeny » Sun Jan 10, 2010 7:22 pm

Is 5 a factor of N?

1) 25 is a factor of 5N
2) 5N is a perfect square

My ans is D. Both in itself are sufficient but the official answer says C.

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Source: Beat The GMAT — Data Sufficiency | Sun Jan 10, 2010 7:22 pm

papgust: Community Manager; Posts: 1537; Joined: Mon Aug 10, 2009 6:10 pmFollowed by: 252 members; Thanked: 653 times

by papgust » Sun Jan 10, 2010 10:46 pm

Even i'm getting D.

1. 25 is a factor of 5N

25=5*5
If 25 is a factor of 5N, N must have atleast one 5. So, 5 is a factor of N.
Sufficient.

2. 5N is a perfect square.

5N to be a perfect square, N must have atleast one 5. So, 5 is a factor of N.
Sufficient.

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linkinpark: Master | Next Rank: 500 Posts; Posts: 124; Joined: Tue Dec 22, 2009 8:32 am; Location: Karjat; Thanked: 3 times

by linkinpark » Mon Jan 11, 2010 9:10 am

N is not mentioned to be integer so I think there is a trap around that

consider in first statement N = 5*root(10) so 5N = 25*root 10
from second if 5N = perfect square and has 25 as factor, will give N to be a multiple of 5.

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linkinpark: Master | Next Rank: 500 Posts; Posts: 124; Joined: Tue Dec 22, 2009 8:32 am; Location: Karjat; Thanked: 3 times

by linkinpark » Mon Jan 11, 2010 9:11 am

by the way forgot to mention in stmt 2 alone you can take N=36/5 so 5N is perfect square

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mehravikas: Legendary Member; Posts: 1161; Joined: Mon May 12, 2008 2:52 amFollowed by: 1 member; Location: Sydney; Thanked: 23 times

by mehravikas » Mon Jan 11, 2010 6:52 pm

I agree that statement 2 is not sufficient by itself but statement 1 is.
According to your explanation if N = 5 root (10) still 5 would be a factor of N

Statement 2 is insufficient because N could be 1/5 5 * 1/5 = 1 which is a perfect sqaure

linkinpark wrote:N is not mentioned to be integer so I think there is a trap around that

consider in first statement N = 5*root(10) so 5N = 25*root 10
from second if 5N = perfect square and has 25 as factor, will give N to be a multiple of 5.

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