It’s the divisor, not the quotient, but it’s best not to think in formulas. Mathematics is about logical thinking, whether it’s numbers or algebraic quantities, or whatever. The subject is hard, boring and confusing if you try to remember formulas, and it becomes a lot easier and much more interesting when you convert the abstract into the practical—see the reasoning that leads you to the answer, and to the formulas.
One of the greatest mathematicians was Einstein and his regular practice was thought experiments, making practical what was abstract. He did this while working in a patent office, presumably because the work was boring, and he needed something to occupy his mind. His relativity theories were derived initially by imagining doing things like riding on a beam of light or riding in an elevator falling under gravity. Then he “did the math” and made some startling conclusions. In his younger years his teachers reckoned he would never amount to much! So, encourage your son to think, and maybe he’ll do great things!