Rule Analysis

The rule states: If a person is drinking beer, then they must be over 18 years old. This can be represented logically as: Drinking Beer $\implies$ Age > 18.

To ensure this rule is followed, we need to check cases that could potentially violate it. This involves checking the contrapositive form of the rule as well: If a person is not over 18 (i.e., Age $\le$ 18), then they must not be drinking beer (i.e., not Drinking Beer).

Checking Each Person

• P: P is 16 years old (Age $\le$ 18). P is not mentioned as drinking beer. To verify the rule, we must check what P is drinking to ensure P is *not* drinking beer.
• Q: Q is 25 years old (Age > 18). Q is not mentioned as drinking beer. This situation does not violate the rule, as the rule only mandates age for those drinking beer.
• R: R is drinking milkshake (not beer). This does not fall under the scope of the rule, which specifically applies to drinking beer.
• S: S is drinking a beer (Drinking Beer). According to the rule, S must be over 18. Therefore, S's age must be checked.

Required Checks

Based on the analysis:

• We must check S's age because S is drinking beer.
• We must check P's drink to confirm P is not drinking beer, as P is underage (16).

Therefore, the checks needed are P's drink and S's age.