A new study from the National Center for Education Statistics found more than half of adults in American prisons lack basic math skills, Inside Higher Ed notes, much higher than the general population. The portion lacking basic literacy was also quite a bit higher.

The study defines “basic” using the Program for the International Assessment of Adult Competencies survey. The folks in this graphic scored below level two, which requires test-takers to find the phone number on a website, and parse a list of trips to find what a truck driver would be paid for a specific day’s work.