Percent http://www.math.com/school/subject1/lessons/S1U1L7GL.html
Converting Between Decimals, Fractions, and Percents http://www.purplemath.com/modules/percents.htm
Proportions: Introduction http://www.purplemath.com/modules/ratio2.htm
Basic "Percent of" Word Problems http://www.purplemath.com/modules/percntof.htm
Solving Percent problems using proportions http://www.glencoe.com/sec/math/prealg/prealg03/extra_examples/chapter6/lesson6_5.pdf
Percent of" Word Problems: Markup and Markdown Examples http://www.purplemath.com/modules/percntof2.htm