3. Which of the following random variables is geometric? b) The number of phone calls received in a one-hour period. b) The number of times I have to roll a six-sided die to get two 5 s . e) The number of digits I read beginning at a randomly selected starting point in a table of random digits until I get a 7 . (e) All four of the above are geometric random variables.

The random variable that is geometric is the one that counts the number of trials until the first success occurs. In this case, option (e) is not correct since the others involve different setups or dependencies. For example, rolling a die until a certain outcome doesn't fit the geometric model unless it's about a single success like rolling a 5 instead of waiting for two occurrences. Looking at the real-world applications, geometric distributions can model situations like the number of attempts needed before getting a favorable outcome, like finding your keys after looking at several places but only counting each unsuccessful attempt until you find them!