Total variable costs do not change within the relevant range of activity.If the activity index decreases, total variable costs will increase proportionatelySunk costs can't be undone, so they are relevant cost.Fixed costs remain constant per unit at various levels of activity.For planning purposes, mixed costs are generally grouped with fixed costs.Break$-$even in dollars is the point at which total contribution margin equals total fixed costs.A target net income is calculated by dividing fixed cost over contribution margin per unitThe margin of safety is the difference between the actual revenue and break even revenueBoth variable and fixed costs are included in calculating the contribution margin.For CVP analysis, mixed costs must be classified into their fixed and variable components