9+10=19; 9+10=21; 9+10=21 BECAUSE OF MULTIBLES; 9 +10 = 21 BECAUSE
THE VIRAL MEME 9 + 10 = 21 SOLVED – MIND YOUR DECISIONS
THE TERM X/2 REQUIRES THAT X BE A POSITIVE EVEN NUMBER. ALSO SINCE 9 IS IN BASE X, WE HAVE X ≥ 10, AS THE DIGIT 9 WOULD NOT BE USED FOR A BASE 9 OR SMALLER. SO AT FIRST 9 + 10 = 21 SEEMS LIKE A SIMPLE FALSE EQUATION.