I am currently using zetamac (has customizable number ranges but doesn't allow for decimals), tradermath (seems to be made to resemble the actual test for flow but costs money unfortunately), and rankyourbrain (has decimal questions but the they appear to be too difficult to be representative).
Note that tools to help you prepare for flowtraders and similar tests are not what I'm looking for since they don't have MC questions. Please hit me up or comment if you know of any alternatives.
I personally used the Secrets of Mental Math by Arthur Benjamin and https://www.tradermaths.com/. However, you should still practice fractions after using both resources as this is not well explained and/or tested in both the book nor the website.
You could write your own. That would allow you to customize it as you wish, and have the double effect of practicing programming.
This is a personal fav of mine, you can customize the operations and range and then practice on different parts: https://arithmetic.zetamac.com/
I would also study tricks to make certain calculations faster e.g.
$52 \cdot 48 = (50-2)(50+2)=50^2-2^2=2500-4=2496$
Check out tradinginterview.com. It helped a lot with my Optiver 80 in 8, it was very accurate.
I'm personally a big fan of OpenQuant (https://openquant.co/math-game). I've found their tests to be pretty similar to tradermath and my friend was able to land a role at Optiver by practicing their exams.
