Questions from official GMAT REVIEW--help--GMAT TOMORROW!

This topic has expert replies
Junior | Next Rank: 30 Posts
Posts: 15
Joined: Thu Mar 27, 2008 4:42 pm
Location: Houston
Thanked: 10 times
Hi guys--two more I couldn't figure out.

144.
If n is a positive integer, is (1/10)^n <less> 2
(2) (1/10)^n-1 <0.1

The answer is D.

But I do not understand how part 2 in itself is sufficient. N could be 0 or 1, in which case the term would not be < 0.1. But if it was 3 or greater, then it would be <0.1. So that makes part 2 insufficient, doesn't it?



The other one is # 146, also in data sufficiency (page337). Here's the question:

Is n an integer?
(1) n^2 is an integer.
(2) the square root of n is an integer.

The answer, according to the explanation, is B. But why isn't A sufficient? if n squared is an integer, then doesn't n have to be an integer? True, it could be negative or positive, but no decimal/fractional value will work for n, therefore it has to be an integer. SO why isn't A alone sufficient, as well as B?

I am wondering if these are errors in the book, or if I am an idiot. Please help!
Source: — Data Sufficiency |

Newbie | Next Rank: 10 Posts
Posts: 9
Joined: Tue Feb 19, 2008 10:04 am
Thanked: 2 times

by mba.dude » Sat Mar 29, 2008 8:03 am
I am not sure if these would help you at this hr or not.. but here are the explanations :

144)
For stmt 2 to be true n has to be greater than 2, as for n = 1 0r 2, the left side doesn't comes out less than right side making the inequality false.

So both the statements alone will suffice.

146)
stmt 1 is not true. For eg: n = square root of any integer, then only n2 square will be an integer.. Hope I am clear.
All the Best!

Junior | Next Rank: 30 Posts
Posts: 12
Joined: Sun Mar 09, 2008 7:03 am

by samb » Sun Mar 30, 2008 9:35 am
Would you be able to be more specific? I'm having problems with that same quesiton as well.

If N^2 is an integer...then N must be an integer, correct? Are there any circumstances where the product of two non-integers equals an integer?

Thanks!

Senior | Next Rank: 100 Posts
Posts: 72
Joined: Mon Mar 10, 2008 10:29 am
Thanked: 25 times

by tmmyc » Sun Mar 30, 2008 10:10 pm
samb wrote:Would you be able to be more specific? I'm having problems with that same quesiton as well.

If N^2 is an integer...then N must be an integer, correct? Are there any circumstances where the product of two non-integers equals an integer?

Thanks!
Think about it this way:

Is sqrt(2) an integer? No, it's 1.4142...

Is [sqrt(2)]^2 an integer? Yes, namely the integer 2.

Just because N^2 is an integer (i.e. 2) does not guarantee that N is an integer (i.e. sqrt(2)).