Porisma

A hint to get started

Normalize a symmetric law and average an absolute distance

The discrete random variable XX has probability function

P(X=x)={k(2−x),x=0,1,2,k(x−2),x=3,4,0,otherwise,P(X=x)=\begin{cases}k(2-x),&x=0,1,2,\\k(x-2),&x=3,4,\\0,&\text{otherwise},\end{cases}

where k>0k>0. (i) Show that k=1/6k=1/6 and state E(X)E(X). (ii) Find E(∣X−2∣)E(|X-2|). (iii) Find Var⁡(X)\operatorname{Var}(X).

[2006/IJC/II/23]

CJC · Lecture · Example 12

Normalize the five masses, then use symmetry for the mean.

Average the absolute distances with their original probabilities.

Find the second moment before subtracting the squared mean.

Read the worked solution