 In the 25th annual "Forbes" list of global billionaires, Slim added $20.5 billion to his fortune, the most of anyone, and retained his number one ranking with a total fortune of $74 billion.Gates remained in second place with $56 billion, while Warren Buffett was third with $50 billion.The top 10 had a combined wealth of $406 billion, up from $342 billion in 2010.