A rule states that in order to drink beer, one must be over 18 years old. In a bar, there are 4 people. P is 16 years old, Q is 25 years old, R is drinking milkshake and S is drinking a beer. What must be checked to ensure that the rule is being followed?

Question

Prepp Team · Accepted Answer

Beer Drinking Rule Analysis

The core of this problem revolves around a specific rule: “in order to drink beer, one must be over 18 years old.” We need to determine what checks are necessary among four individuals (P, Q, R, S) to ensure this rule is being strictly followed in a bar setting.

Rule Enforcement Principles

To effectively check if the rule is being followed, we need to consider two main aspects:

Age of Beer Drinkers: If someone is drinking beer, their age must be checked to confirm they are over 18.
Drinks of Underage Individuals: If someone is known to be under 18, their drink must be checked to ensure they are not consuming beer.

Individual Person Analysis

Let’s analyze each person based on the given information:

P (16 years old): P is 16 years old, which is under the age of 18. According to the rule, P is not allowed to drink beer. Therefore, we must check P’s drink to ensure P is not consuming beer. If P is drinking beer, the rule is being violated.
Q (25 years old): Q is 25 years old, which is over the age of 18. Q is legally allowed to drink beer. Whether Q is drinking beer or something else, it does not violate the rule because Q meets the age requirement for beer consumption. So, we do not need to check Q’s drink or age for rule compliance.
R (drinking milkshake): R is drinking a milkshake. The rule specifically states “in order to drink beer…” Since R is not drinking beer, the age requirement for beer consumption does not apply to R in this context. Therefore, we do not need to check R’s age for rule compliance related to beer drinking.
S (drinking a beer): S is drinking a beer. According to the rule, to drink beer, one must be over 18 years old. To ensure the rule is being followed, we must check S’s age to confirm that S is indeed over 18. If S is under 18, the rule is being violated.

Compliance Summary Table

The following table summarizes the status of each person and what needs to be checked:

Person	Known Information	Rule Application	What Must Be Checked?
P	16 years old (underage)	Cannot drink beer.	P’s drink (to ensure no beer)
Q	25 years old (of age)	Can drink beer or anything else.	Nothing (already complies based on age)
R	Drinking milkshake	Not drinking beer, so age is irrelevant for this rule.	Nothing (rule doesn't apply to this drink)
S	Drinking a beer	Must be over 18.	S’s age (to ensure over 18)

Final Compliance Check

Based on our analysis, to ensure the beer drinking rule is being followed, we must check two specific things:

P’s drink, because P is underage (16 years old) and should not be drinking beer.
S’s age, because S is consuming beer and must be over 18 years old to do so.

Therefore, the necessary checks are “Only P’s drink and S’s age”.