Here are numbers in 2 series:

series A: 0, 25, 50, 100, 150, 200

series B: 0, 20, 33 1/3, 50, 60, 66 1/3

The numbers shown are just a sample of the numbers in the 2 series. The series are equivalent: for any 2 numbers x and y, the series A value is (y-x)/x, and the series b value is (y-x)/y.

I can’t figure out the formula that would give me the equivalent in series B of any number in series 1 (or vice versa). Can anyone help? Thanks in advance.