Many web sites contain explanations of percents and sample percent problems.
This site gives a quick review of the rules for converting between decimals, fractions and percents. This part of the Swarthmore College s NSF supported Math Forum gives answers to questions students had about decimals, fractions and percents. This quiz initially intended as preparation for the SAT test covers a number of concepts related to percents. This site has a review of how to convert between decimals, fractions and percents and it has a chart giving the fractional equivalent of many percentages. The WWW has calculators for working with percents and to compute percent decrease and percent increase.