You've managed to make me as stressed as I would be during an actual math test which I hope is what you were going for lol. I'm personally not a fan of math puzzles, so it didn't resonate too much with me, though regardless of that I think it's a really original take on the theme out of everything I've played so far :)
Echoing the feedback so far, the time constraint is really tight, even if that's by design. One thing I'd do is maybe start with more time, and try to adjust it to the player's performance? Like if the player succeeds in less than 10 seconds the max timer is reduced by 10 seconds, and if they're taking a long time next timer is extended. But I hear you if you're in a "the stress and frustration is supposed to be part of the experience" mindset
I didn't read the page description before playing the game and was a bit confused to be thrown into the action just like that, I find it always useful and good QoL to have an in-game tutorial, although obviously it's not always possible due to jam constraints. Bringing this up just in case