Richest 400 Americans' net worth jumps 13 percent to $1.7 trillion

``The average net worth of the 400 wealthiest Americans rose to a record $4.2 billion, the magazine said. Collectively, this group's net worth is the equivalent of one-eighth of the entire U.S. economy, which stood at $13.56 billion in real terms according to the latest government data. But the 13 percent growth in the wealth of the richest Americans far outpaced that of the economy overall, helping widen the chasm between rich and poor.''