5 variable in total but fixed per unit – a variable expense or cost is variable when related to output; however, when viewed as a unit cost it is a constant. Assume a variable cost of $4,000. If 800 units are produced, the variable cost per unit is $5.00. however if 1,200 units (a 50 percent increase) are produced, the variable cost would be $6,000 (a 50 percent increase); the variable cost per unit remains $5.00