Which statement describes an event in probability?

• A. A specific outcome
• B. A subset of the sample space
• C. The entire sample space
• D. None of the above

Answer: (B)

In probability, an event is a set of outcomes from the sample space. The sample space includes all possible outcomes of the random process, and an event picks out the outcomes that matter for a particular question. So, any event is described by a subset of the sample space.

This view fits many scenarios. For example, when flipping a coin, the sample space is {Heads, Tails}. The event “getting Heads” corresponds to the subset {Heads}. When rolling a six-sided die, the event “rolling an even number” corresponds to {2, 4, 6}. These are subsets of the full sample space {1, 2, 3, 4, 5, 6}.

While a single outcome is indeed a possible event (it’s a subset containing just one outcome), the standard description that covers all cases is: an event is any subset of the sample space. The entire sample space itself is also a subset and thus an event, but the general concept is captured by the subset description.