The distance between the parallel lines $4y-2x+1=0,x-2y+1=0$ is

$2x-4y-1=0$

$2x-4y+2=0$

Formulae: Distance between parallel lines $=\frac{|c_1-c_2|}{\sqrt{a^2+b^2}}$

Distance between parallel lines $=\frac{|1+2|}{\sqrt{4+16}}=\frac{3}{2\sqrt{5}}$.