Casting Out Nines

Photo Credit: WeGraphics

Casting Out Nines

Welcome to Casting Out Nines, a blog for my ideas and opinions on mathematics, technology, and education. I’m Robert Talbert, and I am an associate professor in the Mathematics Department at Grand Valley State University in Allendale, Michigan. To learn more about me and the work I do, please visit my main website.

Casting out nines in real life is a mathematical process for checking errors in multiplication. Back in the day, it was a standard topic in primary schools. I chose this for the name of this blog because blogging for me is crowd-sourced error checking for my ideas, opinions, and experiments. And also, it sounds cool.

If you are looking for older articles

The posts on this website go back to June 2015, but I’ve been blogging since 2005 and have over 1000 posts prior to this date, including four years of blogging for the Chronicle of Higher Education. When I moved to this site, I didn’t port over my older posts1. However, the pre-June 2015 posts are archived at the Chronicle, and you can access them by going to and using the search feature.

I’ve also linked to some of the most popular and searched-for posts from the Chronicle era below.


All opinions here are my own and are not necessarily those of Grand Valley State.

Although I use the intersection symbol in the header for the blog, not all posts are in the intersection of all three of those areas. Technically I should be using the union symbol, but the intersection symbol looks cooler.

Casting Out Nines Top 10 Most Viewed Posts, 2011–2015

These posts are among the top-10 most commented posts during these years, along with seven of the top-10 most viewed posts above.

  1. I didn’t do this, because this current website runs Jekyll on GitHub Pages, and the Chronicle blog ran Wordpress, and at this time I don’t have a good tool that will take all my posts from Wordpress and convert them into Jekyll posts (which are Markdown files). If anybody would like to volunteer to do this, I’ll let you.