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Problemo - Number Problems

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by eaakbari » Thu Nov 08, 2012 11:08 pm
1) If x and y are positive integers, which of the following CANNOT be the greatest common divisor of 35x and 20y?

-5
-5(x - y)
-20x
-20y
-35x
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by sanrisenew » Thu Nov 08, 2012 11:27 pm
as X& Y are positive integers therefore 35y and 20x are best contenders for GCD. 5 is a divisor but definitely not GCD. hence A
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by eaakbari » Thu Nov 08, 2012 11:36 pm
sanrisenew wrote:as X& Y are positive integers therefore 35y and 20x are best contenders for GCD. 5 is a divisor but definitely not GCD. hence A
Substitute x = 1 & y =1 and HCF will be 5.

I got the answer as B, but I used a very long substitution method. I am sure there has to be a better method..at least I hope
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by GMATGuruNY » Fri Nov 09, 2012 4:22 am
eaakbari wrote:1) If x and y are positive integers, which of the following CANNOT be the greatest common divisor of 35x and 20y?

-5
-5(x - y)
-20x
-20y
-35x
Look for an answer choice that cannot be a factor of one of the two values (35x and 20y).

Answer choice C: 20x
35x/20x = 7/4.
Since the result is not an integer, 20x cannot be a factor of 35x.

The correct answer is C.
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