Berkshire Hathaway, the conglomerate run by Warren E. Buffett, reported $11.7 billion in net earnings in the first quarter on Saturday, swinging to a profit from a $49.7 billion loss a year ago as the paper value of its investment gains soared.Using Berkshire’s preferred financial metric, operating earnings, the company showed a nearly 19 percent year-on-year gain as its wide array of subsidiaries — from energy production to the Burlington Northern Santa Fe railroad to consumer brands — improved their performances.Among the businesses that saw the biggest improvements was the railroad, which benefited from higher freight volumes as the American economy rebounded …
