This headcanon makes sense, and I personally really like it. Great job!

This is my new headcanon

Dang I just love when Zoro is being smart

that's so cool! I had never noticed that before!
*hands u a cookie* I love it! Was this just a one shot? If not, I'm excited, but if it is, that's fine. Thanks for the good read!

I'm in love with this headcanon and with this story

That's a nice story! I really like when there's some Zoro-Usopp moments, and it's something we don't see often in fanfictions. And for Zoro being naturally good at maths, it makes sense. I thought about it too when he calculated all those things really fast, in Skypiea or Water 7. I liked reading how the members of the crew discovered about it, and their reactions where kind of funny XD I liked the part with ''because it's the right answer'', it's really the kind of thing Zoro would say.

Anyway, thanks for sharing! I'll be looking forward to read your next stories! ;)

This actually feels very in-character for Zoro, I like it!

Simple mental maths is

DAMNNNNNNNNNNNNN

I like it. I personally think Zoro is actually very smart. There are hints all throughout the manga (like the ones you mentioned and other things) but I think it's more like Luffy where it's just instinct. He's not thinking, 'it's just the answer' like you said. I enjoyed this! You should write more chapters with this theme. It would be funny.