If x and y are positive integers, Choose which of the following CANNOT be the greatest common divisor of 15x and 20y?
Choose one.
A) 5 B) 5(x-y) C) 20x D) 20y E) 35x
We are looking for a choice that CANNOT be the greatest common divisor of 15x and 20y ...which means 15x and 20y when divided by the answer choice the quotient should not be a integer.   lets check   a. 5 15x/5 = 3x and 20y/5 = 4y both are integers so eliminate   b. 5(x-y) when x 20 /5= 
<gadget id="calculator">20 /5</gadget>
<output>4</output>
4y both are integers so eliminate   b. 5(x-y) when x= 2 and y = 1 it could be be the greatest common divisor ..so eliminate   c. 20x when x = 1 its 20 and 20 cannot be the greatest common divisor of 35x and 20y ...   or 15x/20x = 3/4 which is not a integer.   so answer is 20x.
<result>C</result>
If x and y are positive integers, Choose which of the following CANNOT be the greatest common divisor of 15x and 20y?