He may only use reading as a tool for learning what he needs to know. Supplying him with reading material about his interest, such as drawing may result in him reading more. I have found that adults with weak math skills can get the right answer with touch math, counting spots on the numbers. I have found that adults who count rather than add, combine numbers, continue to have weak math skills. They may get the right answer, but it takes too long to complete each calculation.
Mnemonic clues help many individuals to learn the basic number facts.
I am tutoring an 34 year old man who does not know how to read or write. Many individuals who have low level reading and writing skills have learning disabilities that interfere with their ability to learn written language. I find that adults who have poor reading skills avoid writing because of their limited understanding of the structure of language. I do not have beginning readers write. I explain to them that after they have increased their reading skills, we will use these reading skills to help them with spelling and writing.