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original sound - soundeffectpack ... Stupid? No, not. What's 9 + 10? 21, you stupid. TikTok·althea420

: The audio has been mixed into songs, movie trailers, and other viral trends on platforms like TikTok and Instagram. 9 / 10 123movies133...

The story began in 2013 with a short, six-second video that captured a simple yet hilariously confident mistake. In the clip, an older brother is recording his younger brother, who would eventually be known across the internet as the "21 Kid". original sound - soundeffectpack

The video thrived because of its perfect comedic timing and the boy's unwavering confidence in such a clearly incorrect answer. While the actual answer is 19, the boy's "21" became a shorthand for being . What's 9 + 10

Even after the Vine app shut down in 2017, the meme lived on through:

The dialogue that launched a thousand remixes went like this: "You stupid." Kid: "No I'm not." Brother: "What's 9 plus 10?" Kid: (Without a second's hesitation) " 21 ." Brother: "You stupid." Why It Became a Legend