The gap between the richest and poorest Americans widened even as the U.S. economic recovery gained traction in the years after the recession, the Federal Reserve said.

Average, or mean, pretax income for the wealthiest 10% of U.S. families rose 10% in 2013 from 2010, but families in the bottom 40% saw their average inflation-adjusted income decline over that period, according to the Fed's Survey of Consumer Finances, which is conducted every three years.

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