Ask HN: How do I re-learn maths as a middle-age person?

I'm in my early 40s. Recenlty I was looking at one of my old CS textbooks (Mitchell's Machine Learning), and I quickly realised I have forgotten most of my maths, I found much of it impenitrable, despite having no problem with it when I was at university.

It's been 18 years since I've had to do any maths beyond the basics, that was just some trig to do coordinate conversions. Most of the code I've written since uni has been information systems, not mathmatical in nature. I'd love to try my hand at interesting problems, a bit of ML, stats, probability, perhaps simulation or signal processing, and some electronics. But I feel like a carpenter who's forgotten how to use his saw.

I'd really like to regain what I've lost, and perhaps advance a bit more from A-level (that's the 16-18 qualification in the UK). I know I can learn it, I did before.

What are good resources for re-learning maths? I have two small kids so I'd like to find something structured that I can do a little at a time in the evenings, a good book with exercises or an online course would be great.