In the US, this practice is prohibited by the Robinson-Patman Act when it causes “primary line” competitive injury across state borders. Marcel Boiteux (“bwah-TUH”) built upon Frank Ramsey’s finding that this practice may maximize social welfare. The two-part tariff is an example of this practice in which a product has both lump-sum and per-unit components. The third-degree version of this practice relies on an exogenous signal to segment a market. When this practice is performed perfectly, deadweight loss and consumer surplus are (-5[1])eliminated. This practice (-5[1])usually disadvantages consumers with lower elasticities of demand. For 10 points, name this practice exemplified by senior discounts, in which a firm (10[1])charges different amounts to different customers. ■END■ (0[1])