Which of the following is not a discrete random variable?

• A. The number of cars passing through a toll booth in an hour
• B. The amount of rainfall measured in $inches$ during a day
• C. The number of students present in a classroom
• D. The number of heads obtained when flipping a coin $3$ times

Answer: (B)

Verified step by step guidance

1. Understand the definition of a discrete random variable: it is a variable that can take on countable values, often integers, such as counts of occurrences.
2. Examine each option to determine if the variable is countable (discrete) or continuous (can take any value within a range).
3. The number of cars passing through a toll booth in an hour is countable, so it is a discrete random variable.
4. The number of students present in a classroom is also countable, making it a discrete random variable.
5. The number of heads obtained when flipping a coin three times is countable (0, 1, 2, or 3), so it is discrete; however, the amount of rainfall measured in inches can take any value within a range and is therefore continuous, not discrete.