CK-12 Foundation
Ck 12: Algebra: Sets and Symbols
[Free Registration/Login may be required to access all resource tools.] Classify real numbers as rational numbers, whole numbers, integers, and irrational numbers.
Quia
Ixl Learning: Pi
Brush up on your math skills relating to pi then try some practice problems to test your understanding.
Windstream
Ojk's Precalculus Study Page: The Number E and the Function E^x
An introduction to the natural exponential function, beginning with the limit definition of the irrational number e. Includes several examples and exercises with solutions which deal with the compound interest formula.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Rational / Irrational Numbers
Math Forum response providing methods to prove that between any two numbers there exist a rational and an irrational number.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Definitions of Rational, Irrational
Math Forum definition and explanation of rational and irrational numbers, the definitions of mathematics is also addressed.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: About Rational Numbers
Math Forum response giving a rather thorough overview of rational and irrational numbers, with a brief look at the history of these and other number sets.
Other
The Prime Glossary: Rational Numbers
This site gives a definition of what a rational number is. Gives examples and formulas. Very helpful.
Science Struck
Science Struck: Interesting Facts About Pi
Presents many interesting pieces of information from the history of pi.