This is the research field of psychology and education, and I happen to be studying psychology. I didn’t check the relevant literature, so I’ll simply answer your question: there is no necessary connection between the two. The right hemisphere of the brain is responsible for music, and the left hemisphere is responsible for mathematics. They are connected and influence each other. Being good at music exercises his right brain and improves his attention and endurance, which helps improve other subjects such as mathematics. But it doesn’t mean that people who are good at music will be good at mathematics. Everyone’s situation is different. Some children are naturally talented in music but don't like to learn other subjects. They don't have the hard work to learn mathematics well. Some children are good at music, and their families pay attention to nurturing them. They are also interested and can learn mathematics well. This connection is in all aspects and is a correlational relationship rather than a causal relationship. It’s also possible that if you’re good at math, it’s easier to learn music.