180 Days of Ideas for Discussion in Math Class.
(as of 9July2014, we're in overtime!)
Via @mburnsmath, a math mistake. Does it reveal something interesting about how people think about math?
— Michael Pershan (@mpershan) May 4, 2015
There are additional "examples of innumeracy" at the MathEducators StackExchange site: http://matheducators.stackexchange.com/q/1572