system
A chat on subreddit /r/me_irl
human
This is exactly how I do a lot of math quickly in my head, especially for multiplication.

 Say 30 X 17... My brain would go 3X15=45, add a zero, 450, remaining 2x15=30, add to 450=480. 

Or 20x19... 2x2=4, add zeroes, minus 1x20=380

Is this not how all people reason things out? Genuinely interested.

Edit: My error has been pointed out to me. It's late, I'm tired; My bad.
gpt
I hate to break it to you but 30x17 = 510

30x20 = 600
600 - (30x3=90) =510