What does "25% less than X" mean ?

You are both correct, and I misspoke.

x times more than y means (x+1) * y.
x times as many as y means x * y.

However, my primary point, that language cannot always be translated word for word is still relevant.

x times less than y means y / x.

No one uses it to mean y * (1 - x) as several people have suggested that it must mean, based on parallel construction. It’s just not a useful relationship to talk about.

That’s pretty much the point though. Times more than / as many as / times less than…should be easily deducible by parsing the individual words.
If you have to resort to “common usage” then you start to get divergence in language in different communities and situations. Which can’t be a good thing for communication. We should be resisting the dumbing down of math…not promoting it

Language is not math, though. Like I said, I support your interpretation of what it should mean, but it seems that’s not what it actually does mean in English. So, unless I’m trying to be deliberately obtuse or pedantic, if someone tells me “she makes two times more money than I do,” I have to assume that person makes 2X, not 3X. I can’t seem to find any printed reference in which “two times more than” or similar actually means 2X+X (3X). And I was trying to find one for the other thread to support my 2X+X interpretation. It seems that, while logically correct, it’s just not used that way in English.

I never saw the point of becoming a supervillain and taking over the world before. Being so rich that I can’t possibly spend all of my money is one thing; that just means that I’ll always be able to afford to pay somebody to pick up after me. I don’t need to be Ming the Merciless for that (plus, who needs to be always looking over his shoulder for Flash Gordon?).

For the opportunity to exterminate the kind of sloppy use of language in the above quote from the planet, though; THAT might just be worth it.

Dr. Cube wrote that he has never seen a “legit scientist, engineer…etc.” use the phrase something like, five times less than…

I disagree. I have been puzzled about the phrase for years, but only decided to post it here as I have now seen several so-called scientists or engineers use the phrase in published papers. I am sure we could argue without end over whether they were authentically, unambiguously, truly and honestly LEGIT.

The clear answer is obviously absolutely and as they say about everything today - totally - ambiguous.

I see that in addition the correction I made above, I also somehow lost a word from my first sentence. I’m sure I wrote it, so I’m blaming internet gremlins (clumsy copy/pasting).

It should have been: “People seem to really dislike this phrasing, but that doesn’t make it ambiguous”.

Did I miss something else? Are my thoughts really so poorly expressed that they inspire dreams of dictatorship? Are we just running into a prescriptivist/descriptivist divide? It would be nice if language were always completely consistent and logically parseable, but it isn’t.