Expected Value Math Example 1

Follow the full solution, then compare it with the other examples linked below.

Example 1

easy
A fair six-sided die is rolled. What is the expected value of the outcome?

Solution

  1. 1
    A fair die has six equally likely outcomes {1,2,3,4,5,6}\{1,2,3,4,5,6\}, each with probability 16\frac{1}{6}.
  2. 2
    Apply the expected value formula: E(X)=โˆ‘xiโ‹…P(xi)=16(1+2+3+4+5+6)E(X) = \sum x_i \cdot P(x_i) = \frac{1}{6}(1 + 2 + 3 + 4 + 5 + 6)
  3. 3
    Compute the sum: 16ร—21=216=3.5\frac{1}{6} \times 21 = \frac{21}{6} = 3.5

Answer

E(X)=3.5E(X) = 3.5
The expected value is the long-run average outcome. Note that 3.53.5 is not a possible outcome of a single roll, but it is the average over many rolls.

About Expected Value

The expected value of a random variable is the probability-weighted average of all possible outcomes โ€” the long-run mean over many repetitions.

Learn more about Expected Value โ†’

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