Please state in which country your phrase tends to be used, what the phrase is, and what it should be.
Example:
In America, recently came across “back-petal”, instead of back-pedal. Also, still hearing “for all intensive purposes” instead of “for all intents and purposes”.
Reduce TO one tenth?
Nope, reduced by 10%, leaving you with 90% of the original quantity.
Ah, TIL, I thought it was a reduction TO 10%, but I see you are correct!