Posting its third straight day of losses, the Sensex at the Bombay Stock Exchange plunged 288 points, or 1.5 percent, to a 5-month closing low of 18,396, on broad-based selling, on Friday. The market fell as investors continued to fret about inflation and interest rates. The Nifty shed 92 points, or 1.6 percent, to 5,512.Stock markets in Japan, China, Hong Kong, South Korea and Singapore ended mixed.