# Expectation of Bernoulli Distribution/Proof 1

## Theorem

Let $X$ be a discrete random variable with a Bernoulli distribution with parameter $p$.

Then the expectation of $X$ is given by:

$\expect X = p$

## Proof

From the definition of expectation:

$\displaystyle \expect X = \sum_{x \mathop \in \Img X} x \, \map \Pr {X = x}$

By definition of Bernoulli distribution:

$\expect X = 1 \times p + 0 \times \paren {1 - p}$

Hence the result.

$\blacksquare$