National Council of Teachers of Mathematics
The Math Forum: Ratios and Fractions
A seventh-grade student is having trouble understanding ratios, fractions, and simplest form. Dr. Math to the rescue! Real-world, easy to grasp examples.
Purple Math
Purplemath: Proportions: Introduction
Explains the basics and terminology of proportions.
Jim Loy
Jl's Math Page: The Golden Rectangle and the Golden Ratio
This is a personal site from Jim Loy that describes the golden rectangle and the golden ratio. Includes several diagrams and pictures as well as formulas. A good background in math is helpful.