Expected Value Formula

For a discrete random variable X with outcomes x₁, x₂, ..., xₙ and probabilities P(x₁), P(x₂), ..., P(xₙ):

E[X] = x₁ × P(x₁) + x₂ × P(x₂) + ... + xₙ × P(xₙ)

It is a weighted average: each outcome multiplied by its probability, then summed.