Mathematics is a system of learning and reasoning, arithmetic is the process of actually computing an answer. While it might be nice to be able to compute compound interest in your head no one is seriously proposing that anyone do multivariate linear regressions with a pen and paper, we simply have much better tools for computing the answer.
In a modern society with large amounts of non-human computational power it's far more economical for humans to focus more on math and less on arithmetic.
In a modern society with large amounts of non-human computational power it's far more economical for humans to focus more on math and less on arithmetic.