Answer :
If you use the common denominator of .5 for both sides of the ratio, you will arrive at 3:5 as a simplified form.
I usually divide both numbers by the GCF (Greatest common factor of where its a number where it can go into both numbers u looking for) and divide the numbers by that, and for 1:5 and 2:5 it CANT( CAN NOT) be simplified any further since its already simplified in lowest terms.