D'oh! Fake math!
When I was a newspaper reporter and editor, most reporters didn't check their math, especially if a figure was given to them by an official source. That's probably more true now, given that there are few reporters trying to cover more news than ever.
I was considered "good at math" for a writer, which meant I could easily figure out percentage changes and other relevant figures. Like most journalists (now a recovering journalist who's in corporate communications), however, I'm pretty lousy overall at anything beyond basic math.