@Touchstone: friends kept asking me about percentages (I'm sorta good with numbers... better than most, not great). I looked up "percentage calculator" on Google, found dozens of these tools, but they all kinda sucked and were probably hacked in an hour or two (many even didn't do that, there's a free javascript…

@skaneateles: The calculator is not broken, but you're right, the article is wrong. When you enter "5 is 80% decrease from" in the 3rd sentence, it will tell you 25. Adam probably entered 5 is 80% of 6.25 in the 4th sentence (a 20% decrease).