Is the following comma placement correct?
A is twice the number of B and, the closer A is to 0, the closer B is to zero.
Short answer: the first comma is not required. It's useful because you are stacking up three clauses in a row. A better approach, though, would be either to put the first clause in a separate sentence
A is twice the value of B. The closer A is to zero, the closer B is to zero.
You could alternatively use a comma and "and" in place of the full stop.
If you want to express causality (because of the first clause, the second and third clauses are related), it would be use "therefore" or "so" or "and so".
A is twice the value of B therefore the closer A is to zero, the closer B is to zero.
You can put a comma before "therefore" if you like.
The first comma should be before "and" because "and" is joining two independent clauses. It should be written like this:
A is twice the number of B, and the closer A is to 0, the closer B is to zero.