To represent the condition of being at least 18 years old for attending a party in an inequality, x ≥ 18 is the suitable representation based on sufficient and necessary conditions.
Sufficient condition: If a person is legally eligible to buy alcohol in this state, then they are at least 21 years of age. A is sufficient for B means if A, then B.
Necessary condition: A person's being at least 21 years of age is a necessary condition for a person's being legally eligible to buy alcohol in this state. If not at least 21 years old, then not legally eligible to buy alcohol.
Based on these conditions and statements, the criterion 'x ≥ 18 years' can be represented as x ≥ 18 in an inequality.
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