Throw a cubical die into the air, and photograph it with a high-speed camera in midflight. Assuming half the faces are visible in each photo, what is the *average* number of times you would need to throw-and-photograph the die before all 6 faces have been photographed?
[This is inspired by a similar puzzle for a sphere, https://twitter.com/mikeandallie/status/1663710291769557002, for which Mike Lawler and Christopher Long found a very nice solution for any dimension.]