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20. SLM
Fortune 500 rank: 286
2007 loss: $896.4 million

The student loan giant -- best known as Sallie Mae -- got a failing grade last year after Congress got tough on the profits that Sallie makes from federally-guaranteed education loans. The company added about $800 million to its loan-loss provisions from 2006 to reflect the reduction in the rates the government allows Sallie to charge. It lost another $1.4 billion on its portfolio, which was socked by falling interest rates and volatility in the credit markets.

All this led private equity firm J.C. Flowers, which headed a consortium that agreed to buy Sallie in April 2007 for a nearly 50% premium, to eventually walk away from the deal.

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Last updated April 24 2008: 11:01 AM ET