单选题 A store bought 5 dozen lamps at ＄30 per dozen and sold them all at ＄15 per lamp．The profit on each lamp was what percent of its selling price?

A、 20％
B、 50％
C、
D、 100％
E、 500％

【正确答案】 C

【答案解析】For this problem it is especially important to keep your focus on what is asked and to ignore extraneous details.The cost per lamp is $30/dozen=$30/12 and the selling price per lamp is $15, so the profit per lamp is $ (15-30/12). Therefore, for each lamp the profit as a percent of the selling price is