Example · High school

Terms

TermThis exampleWhy
discrete distribution Yes The roll of a fair die has a discrete distribution, because the roll takes one of the $6$ values $1, 2, \dots, 6$.
continuous distribution No The roll of a fair die does not have a continuous distribution, because each of the values $1, \dots, 6$ has probability $\frac{1}{6}$.
mixed distribution No The roll of a fair die does not have a mixed distribution, because all of its probability is on single values.
singular distribution No The roll of a fair die does not have a singular distribution, because single values have positive probability.
probability mass function $p(k) = \frac{1}{6}$ for $k = 1, \dots, 6$ The roll of a fair die has the probability mass function $p(k) = \frac{1}{6}$, because each of the $6$ outcomes is equally likely.
cumulative distribution function $F(x) = \frac{\lfloor x \rfloor}{6}$ for $0 \leq x \leq 6$ The cumulative distribution function of a fair die roll is a staircase, rising by $\frac{1}{6}$ at each of $1, 2, \dots, 6$, because $P(X \leq x)$ counts the outcomes at most $x$.
expected value $\mathbb{E}[X] = 3.5$ $\mathbb{E}[X] = \frac{1 + 2 + 3 + 4 + 5 + 6}{6} = 3.5$. Note: The expected value is not a possible outcome.
median $\frac{3 + 4}{2} = 3.5$ The expected value and the median of a fair die roll are both $3.5$, which is not a possible outcome.
mode Every outcome, $1$ through $6$ Every outcome is equally likely.
variance $\operatorname{Var}(X) = \mathbb{E}[X^2] - 3.5^2 = \frac{91}{6} - \frac{49}{4} = \frac{35}{12} \approx 2.92$
standard deviation $\sqrt{35 / 12} \approx 1.71$

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