Calculating the expectation and variance after a fair die is rolled twice.

expected valueprobabilityvariance

If we roll a fair die twice and if we let $X$ be the maximum of the two rolls, and $Y$ be the minimum of the two rolls. Then I have to compute $\mathrm{E}[X]$, $\mathrm{Var}[X]$, $\mathrm{E}[Y]$ and $\mathrm{Var}[Y]$.

I thought of the following.

Maximum value to appear in the two rolls $X = \max (\text{roll 1}, \text{roll 2})$ gives $X = \{1,2,3,4,5,6\}$ and

Minimum value to appear in the two rolls $Y = \min (\text{roll 1}, \text{roll 2})$ gives $Y = \{1,2,3,4,5,6\}$.

Any help would be grateful.

Best Answer

What you need are the respective frequencies.

On a total of $36$ possibilities, for the maximum,

$$\begin{matrix}1&2&3&4&5&6\\\hline1&3&5&7&9&11\end {matrix},$$

and for the minimum,

$$\begin{matrix}1&2&3&4&5&6\\\hline11&9&7&5&3&1\end {matrix}.$$

The rest is yours.