Edit: it appears that this is not exclusive to ADHD.
Posting this meme stemmed from my own efforts to explain my thought process when doing math and how it is similar to other people with ADHD doing math, while being different from every neurotypical person I'd talked to on the same subject.
While I didn't make the meme itself, instead finding it in my saves and wanting to share, I did accidentally spread misinformation that I had only backed up with personal anecdotal evidence.
I'll leave this up just so people can see the explanation below but this appears to not be ADHD related and just due to different people doing math in their heads differently...
Similarly, when I'm counting stuff I always do
Group of 3 Group of 3 Group of 4
Okay that's 10
Rinse repeat.
It just works very well for me to count lots of things very quickly and easily. I can easily see what a group of 3 or 4 looks like so the whole process is super fast.
12 is a great number isn't it. I remember one especially boring job I had for a while I would spend large amounts of time counting in base 12 on my fingers (using my thumb to tap the three segments of my four opposing fingers) into the thousands and start over.