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A bit OT, but this reminds me of an inspirational mathematics teacher I had, who loved to present the subject as a series of applied problem-solving exercises, rather than the usual learn-by-rote.

One of his problems was: if a 33 1/3 rpm record is 12 inches in diameter and plays for 25 minutes, how wide is the groove?

I had a clear visualisation in my head of the problem, including the groove cut into the vinyl. Watching this is like listening to my teacher speaking to me again.

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