9 + 10

19 is 10 + 9

it is actually 21.

See this elegant proof:

https://www.youtube-nocookie.com/embed/6F6hw_U-AX4?autoplay=1&iv_load_policy=3&loop=1&modestbranding=1&playlist=6F6hw_U-AX4

It's 21.

0+9=9 10+9=19. What is your IQ?  Just wondering.