It's taken me a while to understand what and how Dysclaculia is and how it works. Hopefully, my understanding will help you understand what is happening.
The key to my understanding came when a science research team posted a paper stating that Math and Linguistics are processed in 2 different parts of the brain. And, on top of that Math is not processed the same way that a computer processes math. Or, how we think math is processed. It's not a direct forward process of (1 + 1 = 2). Math, is a guessing game. Is (1 + 1 = 2)?
Think about what is needed to evaluate this question .. Is (1 + 1 = 2)?
Research has shown that language, or more accurately, words and phrases are processed as pictures. When you see the word "Picture" your mind doesn't independently see the various letters, it sees the word, "Picture" in all it's forms. Because, it's seen the word picture in 1000s of forms as you grow up. Initially, you learned how to recognize the letters that form the word, "Picture" . Then you learned how to recognize the word, "Picture", in it's stressed, misspelled and partially spelled forms. You can even recognize the acronym, "PCT", as the world picture.
From the word, "Picture", we expand to phrases. "The picture is on the wall." Even though the sentence is on two lines for me, I can see the sentence as a whole phrase and comprehend it quickly. I can do this because I see the phrase a whole picture, not individual words. (which brings us to Dyslexia, but that's a different topic for another day.)
Now, let's look at that process with a math equation.
In Math, you have individual letters, numbers, and symbols that are all independent. (y = ax + b), (1 + 1 = 2), (y = 2), (a = 3/2), and (b = 2). What is (x)?
In order to read this series of equations and evaluate the answer, and state what (x) is, you first have to recognize all the letters and symbols. But, the next step, recognizing that they form a word, like "Picture" doesn't happen. In fact, this is where most people stop with understanding math, and have to start guessing.
For those that are able to execute Calculus, may say, " I can't have Dyscalculia? Because, I can do high math!" Being able to do high math, only means that after a lot of struggle, you figured out a way to memorize the various operations that are being executed to evaluate the mathematical equations. And, that's the key to the next step in processing math equations.
The scientists found that when we evaluation, (1 + 1 = 2), we are guessing at the answer. We guess with increasing confidence as our systems that help us determine that (1 + 1 is 2). Where as language says, "PCT" is "Picture".
Which now brings us to the rules of math. These rules may be be able to evaluate a statement to true or false, but again, we are still guessing whether or not a rule works the way we think it does.
Take for instance the parenthesis "(" and ")". There are meme's that ask you to evaluate ( ( 5 * (3 + 2) / 4) - 5). What is the answer? What rules do we apply to evaluate this answer? No, I'm not going to evaluate this problem for you. Shame on me. It's here to help you see that math equations cannot be read like sentences. We have to read mathematical equations character by character. It's slower, requires more energy to execute. And, requires a lot more memory to evaluate a mathematical equation. On, top of the number of rules and processes we have to recall to properly evaluate the equation.
All, if not all, of these processes are affected some how in ADHDrs. And, while math is a difficult subject for NTs, it is an extremely difficult subject, even though we may be brilliant at things that look mathematical.
As, we have learned with ADHD, neuro pathways and neurochemistry affect our ability to recall, ability to maintain things in memory, are easily distracted, and have no ability to shunt emotions from the executive function. Thus, our ability to learn the rules, or more accurately, "Memorize the rules" to our associative memories becomes almost impossible.
Thus, if the ADHD brain is lacking the neuro pathways needed in one area, it stands to reason, that they can also be lacking in others. Others, being the area needed to understand and process mathematical equations, for even things that may not look like math equations.
How many hours are in 2 days? Is 48 hours 3 days?
Can you tell me how many seconds are in an hour?
So, if you still find yourself guessing at what the right rule is. Or, what the right answer to a math question is. Just remember, you don't have confidence in your answer yet. If you have the ability to learn other techniques to understand math equations, it will help you build your confidence. If not, then use a program, like SageMath, to help you evaluate mathematical equations.
I hope this has helped you understand what causes Dyscalculia and how to help you manage it better.