I'm reading Jech's Set Theory, and in the chapter about measurable cardinals there is a theorem that if $\kappa$ is real-measurable but not measurable then it is $\le 2^{\aleph_0}$ and so and so. (Corollary 10.10)

How can a cardinal number be real-measurable without being measurable? Can't a measure be "destructed" (as in opposite of constructed) into a trivial $0,1$ measure?

This is a classic puzzle!
The answer is that the probability that the last person ends in up in their proper seat is exactly $\frac{1}{2}$.
The reasoning goes as follows:
First observe that the fate of the last person is determined the moment either the first or the last seat is selected! This is because the last person will either get the first seat or the last seat. Any other seat will necessarily be taken by the time the last person gets to 'choose'.
Since at each choice step, the first or last is equally probable to be taken, the last person will get either the first or last with equal probability: $\frac{1}{2}$.
Sorry, no clue about a physical system.
