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## Homework Statement

Let [tex] x_1,x_2,...x_8 [/tex] be a random permutation of the set [/tex] {1,2,3,4,5,6,7,8} and [tex] S= (x_1-x_2)^2+(x_2-x_3)^2+(x_3-x_4)^2+...+(x_7-x_8)^2 [/tex]

Calculate the expected value of S.

## The Attempt at a Solution

I've given this over an hour of thougt. I have no idea how to approach this.

Thanks

Tal