Math for journalists
Another site to bookmark if you want quick math tutorials: Purplemath.com
Although this is an algebra-oriented site, the geometric formulas review is worth printing out (how do you figure out the volume of a sphere, for instance -- possibly useful in approximating a tanker, for example), as is the section on how to round numbers and significant digits (one of the errors you often see in journalism is overprecision when the underlying numbers don't allow it).
Skip past some of the algebra stuff, scroll down to the word problems section, and you'll find a good section on percentages in word problems (and, after all, word problems is what we journalists do).
(The pointer comes from the Internet Scout Report, one of the best-kept secrets on the Web. Weekly it looks for new sites that are human-reviewed, and then e-mails a summary. The database also is searchable from the Scout Report's Web page. There also is an RSS feed, but I have found it to be spotty, often sending links but no explanations.)