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by das.ashmita » Sat Oct 13, 2012 8:57 am
Simple question.... but I guess i am missing out on something basic. :(


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

OA C
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by Anurag@Gurome » Sun Oct 14, 2012 5:45 am
das.ashmita wrote:Simple question.... but I guess i am missing out on something basic. :(


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

OA C
Greatest Common Divisor (GCD) of 35x and 20y should be a divisor of both 35x and 20y. This implies 35x/GCD and 20y/GCD should be an integer.

Now let us look at each of the answer choices:

(A) 5
If x = y = 1, then 35x = 35 and 20y = 20. So, GCD of 35 and 20 = 5. Here 5 is the GCD of both 35x and 20y. So, this NOT the answer.

(B) 5(x - y)
If x = 3, y = 2, then 35x = 105 and 20y = 40. So, GCD of 105 and 40 = 5 = 5(x - y). Again this is NOT the answer.

(C) 20x implies 35x/20x = 7/4, which is NOT an integer.

So, C is the correct answer.
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