Rupert Murdoch’s 21st Century Fox Inc said on Wednesday it had offered to buy Time Warner Inc, a move that would unite two of the world’s most powerful media conglomerates, but Time Warner rebuffed its offer. Time Warner’s stock jumped 17.3 percent to $83.33 on the New York Stock Exchange after news that Murdoch had his sights on Time Warner, the owner of the Warner Bros. movie studio and cable channels such as HBO and CNN, among other media properties. Murdoch’s cash-and-stock bid was worth about $80 billion, or $85 per share, people familiar with the matter told Reuters earlier on Wednesday.