Final answer:
The variable to represent the number of students needed to form a club is 'x', and the inequality x ≥ 5 shows that the minimum number of students required is 5.
Step-by-step explanation:
To define the variable and write an inequality that shows the number of students needed to form a club, let's assume that 'x' represents the number of students.
The inequality can be written as: x ≥ 5
This means that the number of students (x) must be greater than or equal to 5 in order to form a club.