I've had 4 thus far, all with no math questions.
It all depends on the type of prop shop though. If it is more quantitative (usually those with salary, ala Jane Street, etc), expect math.
In most other cases, have a good story of why you want to trade- very important. What characteristics make a good trader. Obviously know what prop trading is, failure rate in trading. Where you expect to be a few years down the road. How will you support yourself during the first few months or longer when things are rough. If you have past skills that will translate well to trading. High pressure situations you have been in. What you have done to get an overview of trading.
Also, keep up to date with big market news and such. But that should be a given. You should enjoy watching CNBC/Bloomberg, because that is what you will be doing all day as a trader in most cases. One interview a few months ago, I had past market news down cold as well as current events. But I got dinged for not having a good outlook for what will happen in the future. Big mistake, and that is when I ordered the WSJ and kept more up to date
Best of luck