Final answer:
The number of phone calls between New York and California on Thanksgiving Day is a discrete random variable because phone calls can be counted as whole units.
Step-by-step explanation:
The number of phone calls between New York and California on Thanksgiving Day is an example of a discrete random variable. This is because the number of phone calls can be counted and thus has countable values. For instance, there could be 100, 200, or 300 calls, but there cannot be 100.5 calls since a phone call is an indivisible unit. This contrasts with a continuous random variable, where values are obtained by measurement and can take any value in a continuous range.
Qualitatively, as an example, the weight of a book represents a continuous random variable because weights can be measured to a fine scale and are not countable. Meanwhile, the number of books in a backpack is a discrete random variable since books can only be counted as whole units.
Similarly, in the context of probability distributions, a discrete probability distribution function assigns probabilities to countable outcomes such that each probability is between zero and one, and the sum of the probabilities equals one.