Arithmetic is another word for math, specifically the areas of math having to do with numbers and calculating.
If you're good at adding, subtracting, dividing, and multiplying, then you're good at arithmetic, which is a big part of math. Arithmetic has to do with doing calculations. To answer most math problems, including almost all word problems, you need arithmetic. The most basic arithmetic is 2 plus 2, but as anyone who's ever taken algebra can tell you, it can get a lot more complicated than that.
Definitions of arithmetic
1
n the branch of pure mathematics dealing with the theory of numerical calculations
 Types:

algorism
computation with Arabic figures
 Type of:

pure mathematics
the branches of mathematics that study and develop the principles of mathematics for their own sake rather than for their immediate usefulness
adj relating to or involving arithmetic
 Synonyms:
 arithmetical