Re: Topic 2 DQ 2 Ilainee and class, costs are classified by the way they vary with business activity. The four major cost behavior patterns are variable costs, fixed costs, mixed costs, and step costs. Variable costs change in direct proportion to changes in business activity. Fixed costs remain constant over a wide range of business activity. Mixed costs contain elements of both fixed and variable costs. A step cost remains fixed over a short range of business activity. Class, what happens to variable costs per unit and fixed costs per unit as volume increases