I'm about to turn 40. I did algebra, trig, and stats in high school (no calculus), then did a BA and PhD in psychology, with a focus on the neural basis of visual perception. Tons of courses on stats and data analysis. After that, I did two post-docs in cognitive neuroscience labs before leaving academia. Had to teach myself some calculus along the way to do my work, but my knowledge is pretty superficial. I would say that I have a solid background in statistics, data analysis, and modeling of functional brain data, but overall my background in math is pretty weak. I would like to strengthen my background in math, but I'm busy with work and family and I don't have the time or desire to back to school. What would be the best approach here?