United Nations Development Program Administrator Helen Clark, center, waits to be introduced at the Chamber of Senators in Mexico City, Thursday, March 14, 2013. The U.N. says the

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United Nations Development Program Administrator Helen Clark, center, waits to be introduced at the Chamber of Senators in Mexico City, Thursday, March 14, 2013. The U.N. says the proportion of the world's middle-class living in developing nations more than doubled between 1990 and 2010 and is expected to be more than 80 percent by 2030. (AP Photo/Alexandre Meneghini) less 

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Associated Press
Fri, Mar 15, 2013 4:06 AM EDT