The number of available web sites devoted to percents gives an indication of the importance of this topic.

Percent
Finding the percent of a number.
http://www.aaamath.com/pct61a-pctnum.html

The meaning of percent with Links to other topics dealing with percents.
http://www.aaamath.com/B/pct.htm

Major Math Homework Checker
This site gives a description of proportion problems and includes an interactive program for solving proportions.
http://www.majormath.com/prealgebrapercent2.htm

Determining Percentage
This is an excellent site offering instruction, practice, play, and exploring.
http://aaamath.com/pct61b-pctnumnum.html

Fractions to Percents
This is an excellent site offering instruction, practice, play, and exploring.
http://aaamath.com/pct61c-fract2pct.html

This is also an interactive site which might help you check your homework.
http://www.majormath.com/prealgebrapercentsadvanced.htm

Percents to Fractions
This is an excellent site offering instruction, practice, play, and exploring.
http://aaamath.com/pct61d-pct2fract.htm

Decimals and Percents
This is an excellent site offering instruction, practice, play, and exploring.
http://www.aaamath.com/pct61e-deci2pct.html

Percents to Decimals
This is an excellent site offering instruction, practice, play, and exploring.
http://aaamath.com/pct61f-pct2deci.htm