Looks like math mistake. From Ameritrade:
"H.J. Heinz Company (HNZ): Berkshire Hathaway and 3G Capital will acquire H.J. Heinz Company (HNZ) in US$28 billion, according to the announcement of Heinz on February 14. H.J. Heinz Company (HNZ) shares began the trading session with a price of US$72.46 and throughout the session climbed to a high of US$72.61. When day-trade ended, the stock finally plunged 19.87% to US$72.50. The stock traded 64.00 million shares in the last trading session, much heavier than its daily average of 1.49 million shares. Investors may want to find out where HNZ will go from here."