It's surprisingly not as hard as you might think. The brain is quite good at adapting. As a simple example, some here have mentioned shopping. I know enough to make a damn good estimate about price differences on special offers, and I have been shopping for myself for 32 years. It's amazing how accurate I am now.
I used to always pay with notes pre cashless society, to avoid faffing with change, but as with everything else, experience means you find your own way to do it. There's only a certain number of coin combinations it could be. I know the combinations.
This will surprise you, but I used to work in a small resort shop. We used to accept Euros. We had the latest exchange rates on a sign on the wall. I could accept Euros and give English change where colleagues struggled, because I understood all I had to do was put the English value of the Euros handed to me into the till. I was giving English change. All I had to do was read the sheet. Others got into a right mess trying to work it out in their heads when everything they needed was in front of them. I have to think differently, find the 'cheat' if you will. Not being able to understand the way everyone else does things can mean I am not encumbered with an inability to find another method.
It's all about paying attention and using the skills I do have to compensate. Budgeting is actually really simple when you make it so. All I need to understand is receipts must be higher than outgoings. I am not completely number blind in that I understand that 9 is greater than 5 for example (some with dyscalculia don't). I am very good with home finance because I understand income and expenditure.
Mortgages somebody else mentioned, again, why do I need GCSE maths to understand what I needed to pay a mortgage and bills? My husband and I have now paid ours off after 25 years because we earned enough to meet the monthly payments between us. What more did I need to know?
I understand APR because unlike some folk who have got maths GCSE, I read the small print. I've never had a payday loan, but I absolutely understand the whopping number they put next to the letters 'APR' in the tiny print on the advert.
Same with credit cards. All I actually need to know is that I must pay it off every month. If I knew I wouldn't be able to do that, I wouldn't be using the card that month. It's surprising how many people with much better maths brains than me, and that GCSE we can't apparently do without don't understand interest on things like store cards. I do. I couldn't do the precise calculation but I understand the concept that if you run up a debt on it you will have to pay back more than you would if you paid promptly.
It's about maximising what I do understand IYSWIM. Of course, there's things I can't do, like people with other disabilities. But I have never been out of work, in debt aside from a mortgage, I have savings and a pension, like most people with that magic grade I haven't got. On the whole, it really hasn't made much difference. Let's face it, a grade C, or 4 as it is now wasn't exactly going to see me on the path to some Megabucks finance job, or get me on course to be a brain surgeon.
Luckily, I could still do a degree because they weren't as fussy when I was doing it about me having maths to study English Literature. I know that's changed now, and I understand why, but it's daft to close doors to bright people who excel at a subject because they can't do another.