Tenet Healthcare Corp. has announced it swung to a third-quarter profit on an investment sales gain, but lowered its outlook as patients struggled to pay bills amid a worsening economy. The company earned $104 million, or 22 cents per share, after a loss of $59 million, or 12 cents per share, a year earlier. Revenue rose 6% to $2.16 billion. Excluding a $140 million gain from the sale of an investment and other items, the company lost 6 cents per share. That and the outlook sent shares plunging more than 25% to $3.01 during the trading session, their lowest point in a decade.