Which of the following is a discrete random variable?

• A. The number of heads obtained in 5 coin flips.
• B. The height of a person in centimeters.
• C. The time required to complete a task.
• D. The weight of a randomly selected fruit.

Answer: (A)

Discrete random variables take on a countable set of values, usually integers like 0, 1, 2, and so on. The number of heads you get in five coin flips fits this perfectly: after five flips, the possible counts are exactly 0, 1, 2, 3, 4, or 5. Each outcome is a distinct, separate value, so it’s a discrete variable.

Height in centimeters is measured on a continuous scale, meaning it can take any value within a range (including fractions). Time to complete a task is also continuous, since you can measure it to arbitrarily fine precision. Weight of a fruit is likewise continuous for the same reason. Therefore, the count of heads in five flips is the discrete example.