For me, math IS difficult. I don’t think that I innately lack ability, but I was subjected to some very poor teaching during a critical time in my elementary school years.
After saying that, I don’t think that these “math errors” are really due to a difficulty with numbers. What I’m seeing is a difficulty with critical thinking, period. Knowing when things don’t “add up” doesn’t require great math skills, just logic and common sense (which is rather uncommon).
IF you really want to rectify that, Khan Academy will accomplish that. Mrs. BN, at the age of 64, was working on-line to complete her Bachelor of Science degree. She failed her College Algebra assessment test and was required to take Remedial Math. Nearly 50 years after her last Math class!
Khan Academy and a few other YouTube math videos made it possible for her to pass all three math classes and graduate Magna Cum Laude!
(How could someone that smart marry a klutz like me?)
FREE!
A simple calculator can easily circumvent arithmetic issues, of course. Mathematical processes require a little finesse. If you want to learn math, and it is good for your brain, just find tutorial materials in books or online. Teaching yourself is actually better than classes.