In recent years, activity-based costing (ABC) has become a popular cost and operations management technique to improve the accuracy of firms' product or service costs in order to help the firms stay competitive. Since the product-mix decision is an important ABC application, most studies in the ABC literature were generally focused on the effect of ABC analysis on the product-mix decision or product cost calculation. However, these studies usually ignored some important factors, such as: capacity expansions, management's degree of control over resources, purchase discount, and change of product's price. Hence, in this paper, we consider these factors to propose a more general model. This model can help managers to make a product-mix decision and identify excess resources so that managers can redeploy them to optimise resource usage. Furthermore, since previous studies did not consider the impact of price changes on product-mix decisions, this paper also examines the impact of reducing product price with different price elasticity of demand (D) on the simulated company's profit.