Symbol manipulation via token prediction, they aren't particularly good at math because of this.
Chain of Thought can help
Send it out to an interpreter like python or wolfram
tl;dr they are not doing math the way we think of math, they for sure do not do calculations like we do in code or calculator
They do it like we do mental math. That's why they aren't so great at math compared to their other abilities. When they are allowed to use calculators, or programs that they wrote themselves, they will be better like us when we do those things.