If you meant *Arithmetic,
Arithmetic: Basically involves adding, subtracting , multiplying , and dividing.
Algebra: Algebra is part of mathematic level, in which it has to do with finding variables, (usually uses symbols in place of values - like finding the x) functions, and also has to do with graphing.
Average: Average is a number that basically means set of numbers relating to function. Like relating to arithmetic.
Hope this helps!!