Jaguar36608 Posted April 10, 2009 Share Posted April 10, 2009 If x and y are positive integers, which of the following CANNOT be the greatest common divisor of 35x and 20y? A. 5 B. 5(x-y) C. 20x D. 20y E. 35x I am always making mistakes with GCD. Please help me with a simple solution. Thanks. Quote Link to comment Share on other sites More sharing options...
tytyros Posted April 10, 2009 Share Posted April 10, 2009 This is a cannot be question so opposite of this question is what could be the GCD ? 35x = 5 * 7 * x 20Y = 5 * 2*2*y GCD will be for sure a multiple of 5 but for every possible answer, 35x/possibility and 20y/possibility should be an integer, for 5(x-y) you can verify this with example 1. 5 ...for sure 5 could be GCD 2. 5(x-y) ,....if x=3 y=2 then 5 * 1 = 5 GCD and the numbers are 75 and 40 GCD of which is 5 ! 3. 20 X ....hold this 4. 20y ....what if x = 4 y then GCD of 35 x and 20 y is 20 y 5. 35 X ....what if y= 28 x then GCD is 35 y Odd one is choice 3 OA please Quote Link to comment Share on other sites More sharing options...
seahawk Posted April 11, 2009 Share Posted April 11, 2009 20x it is ;) Quote Link to comment Share on other sites More sharing options...
avixorld Posted April 12, 2009 Share Posted April 12, 2009 other that this trial and error (by which I also solved it though :-) ) is there any mathemetical way of doing this ? Quote Link to comment Share on other sites More sharing options...
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