Let's use the same experiment/random variable as in the previous example, namely the number of heads one observes after flipping two coins. Recall we have the following table for our discrete probability distribution

Outcome \(X\)	Probability \(P(X)\)
0	0.25
1	0.50
2	0.25

To calculate the mean we need only multiply each outcome \(X\) with it's corresponding probability \(P(X)\) then sum all of these values.

First we multiply

\(X\cdot P(X)\)

\(0\cdot 0.25=0\)

\(1\cdot 0.50=0.50\)

\(2\cdot 0.25=0.50\)

Now we sum all these

\[0+0.50+0.50=1\]

That is the average number of heads we observe is 1.