Suppose, you have
Then y is 25% more than x, if x is used as the "base" value. If y ist the base, then x is 20% less than y.
So if I want to say, that the difference between x and y is ... percent, what value could I use? I can think of using 22.5% being in the middle between 20% and 25%, but that does not feel well-founded.
Should I not use percentages at all?