What is a random variable?

• A. A deterministic number produced by a random process.
• B. A random process that yields only binary outcomes.
• C. A random variable is a function that assigns a numeric value to each outcome of a random process.
• D. A parameter that scales data.

Answer: (C)

A random variable is a function that assigns numeric values to each outcome of a random process. In other words, it takes every possible result and maps it to a number, so you can work with probabilities and measures like expectation and variance.

For example, when you roll a six-sided die, a common random variable is the face value itself. Each outcome 1 through 6 is assigned the corresponding number, so the variable can take values 1, 2, 3, 4, 5, or 6 with equal probability. Another example is an indicator variable that equals 1 if the roll is even and 0 if it’s odd; it assigns a 0 or 1 to each outcome, illustrating that a random variable can be discrete or continuous depending on the rule.

This idea is more than just the single number you observe in one trial. The random variable defines the rule for mapping all possible results to numbers, which is what lets us describe the distribution of outcomes and perform statistical analysis. A single deterministic number from one run is just one possible value, not the whole concept. A Bernoulli process with binary outcomes is a specific kind of random process, not the general notion of a random variable. A parameter that scales data is a different concept altogether.