By Medha Singh (Reuters) -The blue-chip Dow Jones Industrial Average tumbled on Friday, on pace to confirm that it has been in a bear market after it fell 20% from its January record high. The Dow would be the last of the three main indexes to gain the bear market status after the S&P 500 notched that grim milestone in June and the Nasdaq in March. If the Dow closes below 29,439.72 points, it would confirm a bear market that began from Jan. 4, according to a widely used definition. The renewed selling pressure in markets comes in a week that saw the U.S. Federal Reserve raise interest rates by…