So for the past few months I've been telling my kids that, every time they write $latex (x+y)^2 = x^2+y^2$, they kill a puppy. In fact, I will hereafter refer to that equation as the **Dead Puppy Theorem**, or DPT. Since its discovery in early September, my students' usage of the DPT has accounted for more canine deaths than heartworms.

# Tag Archives: modular arithmetic

# Paraskevidekatriaphilia

It's going to be a bit of a strange year for Friday the 13ths. First of all, there will be three of them. Now that's not *especially *weird--it happens every few years--but it's the first time since 1984 that they'll be spaced precisely 13 weeks apart. It's also the last time until 2040 that we'll have three of them in a leap year. I got all this information from a story on the *USA Today* website, which featured some words from one Dr. Tom Fernsler of the University of Delaware, a math professor (naturally) who's earned himself the nickname of "Dr. 13." An interesting tidbit from the good doctor, and bad news for the phobic: the 13th of the month is actually more likely to occur on a Friday than any other day of the week--688 times in a 400-year period.