The Musical, Mathematical Genius in You

Hum a note to yourself, even just in your head. Any note will do.Now double the frequency of that note, and hum that."How on Earth," you're likely asking, "am I supposed to know the frequency that corresponds to this random note? How am I supposed to know what twice that would sound like?"Someone with perfect pitch and a good deal of experience in music could probably sing you 440 hertz--A above middle C--because that's a tuning standard. But would they know what 220 hertz sounds like, or 880?It...