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Director
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Is 30 the factor of n? A. 30 is the factor of n^2 B. 30 is [#permalink]
 18 Feb 2004, 22:28
Question Stats:
0% (00:00) correct
 0% (00:00) wrong based on 0 sessions
Is 30 the factor of n?
A. 30 is the factor of n^2
B. 30 is the factor of 2n
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SVP
Joined: 30 Oct 2003
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I guess C is the answer.
A) if n = sqrt(30) n^2 = 30 divisible by 30 but n is not
if n = 30 then n^2 = 900 divisible by 30 and n is also divisible by 30
B) if n = 15 then 2n= 30 divisible by 30 but n is not
if n = 30 then 2n = 60 divisible by 30 and n is also divisible by 30
Combine these two
n^2 = x * 30
2n = y * 30
Since x and y are integers n has to be mutiple of 15 and 2
Last edited by anandnk on 19 Feb 2004, 13:42, edited 1 time in total.
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Director
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Any one else want to take a look at this problem?
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Director
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Here is our way(Anand + mine) to sove this problem.
From 1: n^2 = a * 30; where a = integer
"a" could be 1 or 30; so n could be fraciton sqrt(30) or 30; NOT SUFF
From 2: 2n = b * 30 ; ==> n = b* 15 ; where b is an integer
b could be 3 or 2 ; (assume)
If b=3 ; then n = 45 ; 30 is not a factor;
If b=2; then n = 30 ; then 30 is a factor;
NOT SUFF
From 1+2:
n^2 = a * 30 --- (1)
2n = b * 30
n = b * 15 ---- (2)
sub (2) in (1)
b^2 * 15^2 = a * 30
b^2 * 15 = a * 2 -----(3)
where both "a" and "b" are integers.
For egn (3) to be valid, 30 should be a factor of "a" and 4 should be
a factor of b^2 or 2 should be a factor of "b".
So; "a" could be any number multiple of 30
"b" could be any number multiple of 2.
a = y*30 and b = z * 2
putting these values back in (1) or (2) proves
that
30 is a factor of N.
If we assume that N is an integer than the answer is A.
But, that is not given in the question stem.
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SVP
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Good explaination kpadma. Just the way we went over it.
Well there is not much time to do this on real GMAT. Some of the steps kpadma has written have to be done in the brain. You can tell just by few steps what will come next.
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close
