The Dow Jones Industrial Average plummeted more than 400 points in the first 10 minutes of trading Friday morning. The selloff comes as global markets are reeling from the United Kingdom’s decision to leave the European Union, which was made official early Friday as the votes were counted in the country’s historic referendum. As the results were being announced, the British pound fell to a 31-year low. The Nasdaq and S&P 500 were also down by almost 3 percent in the initial minutes of trading.