What are 2 fractions with a difference of 1/5 but with neither denominator equal to 5?

notice, again, we use the decimal format of the percentage, 25% is just 25/100 or 0.25 and so on

so.. hmmm the quantities, of 4 + x, must add up to y, thus
4 + x = y

and their concentration amount, must add up as well

1.00 + x = 0.5y

thus    

solve for "x"