What Are Those??? If 9+10=21, then am I stupid, or not? Because someone who was older than me by about ten yearssaid I was. Also, What Are Those?????

no you aren't stupid. I'm not sure what's going on with those numbers though. I've seen them before I don't understand how 9+10=21 though 

9+10=19   always did and always will

People just think it is funny to tell you stupid things. 

They think it is  even funnier when they can see your confusion.

It is kind of funny I guess, I am smiling as I write this post.  :D

he is not being serious, he is referring to a video on youtube: https://www.youtube.com/watch?v=OLBOn0Whhyc

That's a lie. Y'all are teacing this youngin wrong. 9+10=21.