Under the category of arithmetic, there exists GRE Questions on the topics such as Integers, Fractions, Exponents and Roots, Decimals, Real Numbers, Ratio, Percent. Arithmetic begins with integers, fractions, and decimals and progresses to the set of real numbers. The basic arithmetic operations of addition, subtraction, multiplication, and division are asked, along with exponents and roots. And finally there are questions ratio and percent. Topics such as real number and exponents and roots are also under the purview of arithmetic

Arithmetic
Number Properties
Fractions,Ratios and Decimals
Remainder
Divisibility
Percents

It is easy GRE questions on algebra. They include Algebraic Expressions, Rules of Exponents, solving Linear Equations, Solving Quadratic Equations, Solving Linear Inequalities, Functions, Coordinate Geometry, Graphs of Functions. You should note that coordinate geometry is very much part of algebra. Some of the more difficult GRE questions exist on inequalities and absolute values. GRE question on functions mostly cover single variable functions.
Algebra
Sequences
Inequalities
Absolute values
Coordinate Geometry

GRE question on the topic of "Word Problems and Rates Problems" are broadly speaking application of algebra. The main skill that students require is; mapping the given text of the problem to an algebraic expressions. The work and rate problem are similar to word problems. The basic requirement is the ability to map the text to an algebraic expression.

Word Problems
Work Rate Problems
Mixture Problems

GRE questions on probability are some of the toughest problems on the test. Probability is a way of describing uncertainty in numerical terms. statistics on the GRE include topics such as distributions of Data, Random Variables, and Probability Distributions. Finally counting; when a set contains a small number of objects, it is easy to list the objects and count them one by one. When the set is too large to count that way, and when the objects are related in a patterned or systematic way, there are some useful techniques for counting the objects without actually listing them.
Probability
Counting
Graph and Illustration
Statistics
Overlapping set and Venn Diagram
Data Analysis

Although this is closely related, conceptually to statistics, GRE questions on Data Interpretation have a special place in this forum. This is so because on the GRE there are 3 dedicated DI question per quant section. This requires special attention and also quite often it helps boost scores. Special strategies are needed for these questions and we have a dedicated forum for that purpose.

Forum> Data Interpretation

GRE questions on geometry topics include lines and angles, triangles—including isosceles, equilateral,and special right triangles—polygons, circles, multiple figures, three-dimensional figures (uniform solids), area, perimeter, and volume. You do not need to know how to do geometry proofs for the test. The geometry tested on the GRE is basic. There are only a few fundamental definitions and formulas you need to know. The GRE emphasizes new ways of applying these elementary rules.

Geometry