The Brits add the “s” to math...like adding the “u” in color or favorite. Maths, colour, favourite.
They shorten it from “Mathematics”.
It’s one of their many incorrect ways they destroy the English Language. They think because it’s named after them they can butcher it any way they want. //sarc
So, to pronounce these words properly, the "-our" must be pronounced like the word "our."
Thus, they would be pronounced "cuhl-ahr" or "cuhl-ow-er," "fav-ahr-it" or "fav-ow-er-it." I literally do read them that way when I see those extraneous letters that the Brits love to insert into words.