There's an old joke about journalists and math.
I'm not entirely sure what that joke is, but I'm assured there is one and the punchline is that we suck at it.
With all due respect to those who specialize in journalist humour (do these people exist?), freelancers tend to get quite good at maths, though in a particularly specialized way.
I'm sure there are those among our ranks who are quite good at reading spreadsheets and financial statements and making sense of the digits. Personally, I've gotten quite good at a different kind of arithmetic.
With no regular pay cheque, I've taken to memorizing some numbers and repeatedly doing some additions and subtractions in my head. Current bank balance, outstanding invoices and expenses.
It's awfully hard to come up with a budget when income varies wildly month to month.
This is not a complaint, but it is a necessary survival strategy that affects your day-to-day. When you're in the grocery store on a slow month, you need to decide if you really need to upgrade from Kraft cheese to nice gouda. Do you push your friends to go to the nice bar with craft beer? Or do you get the $12 pitcher of Molson draft at the crappy dive?
These are the decisions they definitely did not teach me about at j-school.