Documents X i = indicator random variable of the event that i-th person gets his hat back. E[X i ]=1/20 X=X 1....

Slide 1 X i = indicator random variable of the event that i-th person gets his hat back. E[X i ]=1/20 X=X 1 +…+X 20 E[X] = E[X 1 ] +…+ E[X 20 ] = 1 Slide 2 derangement…

Documents X i = indicator random variable of the event that i-th person gets his hat back.

Xi = indicator random variable of the event that i-th person gets his hat back. E[Xi]=1/20 X=X1+…+X20 E[X] = E[X1] +…+ E[X20] = 1 derangement = permutation with no fixed…