Question 17282
I think I see an error. 


You wrote:

5x - 2y = -5
y - 5x = 3 
-2y = -5x - 5
y = 5x + 3 
-y = 2 


The last line above should be -y = -2, so y = 2.


Then in your next line, I think you made another mistake by substituting the value of y in place of the x.  That's a common error!


Now I think it should be this way to finish:
 5x- 2y = -5
5x - 2(2) = -5
5x - 4 = -5
5x = -1
x  = -1/5


Check:  y -5x= 3
2 -5(-1/5)= 3
2+1= 3
It checks!


In answer to your question, YES a fraction CAN be use, and in this case it MUST be used.  


R^2 at SCC