I was probably teaching statistics the second or third time around when I finally stumbled upon a good understanding the idea of "random." I had once thought that randomness meant a complete lack of predictability, that there was actually no pattern underlying outcomes. However, I eventually realized that predictability is exactly what randomness is about. If I flip a coin, I can expect it to come up "heads" half of the time, thus giving me a "random variable" that is actually quite predictable. For example, out of ten flips of a coin, one might expect five of them to come up heads.

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