Inside the concept of demand and supply, demand basically stands for the customer’s desire to purchase goods and services. In other words, it could be calculated as the price the customers are willing to pay for the goods and products. A simple principle exists for demand, which is when the price goes up, the demand drops; while the price goes down, the demand rises. For example, Mr. James is running out milk for breakfast at home, so he comes to the supermarket to buy milk. In this case, his demand is to buy the milk. However, if the price for the milk rises, the demand for the milk will drop since Mr. James does not want it to be expensive; but when the price falls, the demands for Mr. James will rise since he wants to buy the same product when it is cheaper.