Final answer:
The variable added to a less-than-or-equal-to constraint to convert it into an equality is known as a slack variable, and this action involves the addition of that variable.
Thus, the correct option is 2.
Step-by-step explanation:
A variable added to the left-hand side of a less-than-or-equal-to constraint to convert the constraint into an equality is known as a slack variable. The process involves addition because you add the slack variable to the less-than-or-equal-to side to balance out the inequality, turning it into an equation.
For example, if you have the constraint x + y ≤ 10, you would add a slack variable, let's call it s, to the left-hand side to make the constraint an equality: x + y + s = 10. It is important to remember that s ≥ 0 because you cannot have negative slack in the context of the constraints.
Therefore, the correct option is 2) Addition