I pick 4 numbers from the Uniform Distribution. I need the expected value of the sum of the 3 largest. I am pretty sure that the answer is 9 / 5 which agrees with a simulation. I would like to get mathematica to do this. I have tried this:
Assuming[a >= b >= c >= d,
Expectation[a + b + c, {a, b, c, d} \[Distributed] UniformDistribution[{{0, 1},{0, 1}, {0, 1}, {0, 1}}]]]
which returns 3 / 2. What am I doing wrong?