The Sensex at the Bombay Stock Exchange plunged 292 points, or 1.6 percent, to close at a four-month low of 18,510, today, on across the board selling, on concerns over economic growth and corporate earnings. The Nifty at the National Stock Exchange dropped 98 points, or 1.7 percent, to 5,575.Stock markets in Japan, South Korea and Singapore ended mixed. The markets in China and Hong Kong were closed for a holiday.