Not Quite 11 Triangles

A few mornings ago, my son and I were sitting on the couch waking up to the day. I was sipping my coffee and he was just staring up at the ceiling.

He broke the silence to ask me, “Dada, did you know that there are 11 triangles you can make with the lights on the ceiling?”

I was so proud that my son was entertaining himself with combinatorics problems that I hated to have to tell him he was off a little in his count. (Although he found his mistake right away when I did.)