TITLE: What does $\left|\bigcup\limits_{n=0}^{10}\{n\}\right|$ suppose to be?
QUESTION [7 upvotes]: What "11" on this clock is supposed to be?
it looks like the union symbol but I don't get it.

REPLY [2 votes]: It's the cardinality of the union of all the singlets containing $n$.
So it's the cardinality of the set ${\{0,1,..,10}\}$ which is $11$.