Operating profit ratios of most large South Korean companies fell last year in the face of tough economic challenges, a report by a local conglomerate researcher said Monday. According to Chaebul.com, sales and operating profits of 84 listed affiliates belonging to the country's top 10 business groups, excluding financial firms, reached 695.3 trillion won and 48.6 trillion won, respectively, in 2013, up 2.3 percent and 2.5 percent from the year before.