 Berkshire Hathaway BRK.A, -1.05 BRK.B, -0.74 struck an 11.6 billion, all-cash deal to buy property-and-casualty reinsurance company Alleghany Corp. Y, -0.08 , the companies announced Monday. The 848.02 per share price is 1.26 times book value as of Dec. 31 and a 29 premium to its average price over the last 30 days, the companies said. 