Independent solution

How to solve this Expectation of a Function question

Setup

Setup

Rewrite absolute deviation as signed deviation plus twice its negative part.

X2=(X2)+2(2X)+|X-2|=(X-2)+2(2-X)_+

Model

Model

The density is symmetric around 3, so its mean is 3. Only values below 2 contribute to the correction.

E[X2]=32=1\operatorname{E}[X-2]=3-2=1
u=X1on the correction intervalu=X-1\quad\text{on the correction interval}

Compute

Compute

Evaluate the correction from its polynomial antiderivative, then add it twice to the signed deviation.

E[(2X)+]=14[u22u33]01=124\operatorname{E}[(2-X)_+]=\frac14\left[\frac{u^2}{2}-\frac{u^3}{3}\right]_{0}^{1}=\frac1{24}
E[X2]=1+2(124)=1312\operatorname{E}[|X-2|]=1+2\left(\frac1{24}\right)=\frac{13}{12}

Answer

Answer

The expression with these three intervals and signs is choice E.

(E)\boxed{\text{(E)}}