Resolution Criteria

This market will resolve based on the correct mathematical answer to the addition problem "9 + 10" in standard base-10 arithmetic.

Background

The question "What's 9 + 10?" references a popular internet meme from a 2013 Vine video where a young boy incorrectly answers "21" when asked what 9 + 10 equals. This video became viral and spawned numerous remixes, references, and jokes across social media platforms.

In standard base-10 arithmetic (the number system we use in everyday life), 9 + 10 = 19. The answer "21" from the meme is mathematically incorrect in base-10, though it could be correct in other number systems such as base-4.

I want to see what the real answer is.