The Dow Jones Industrial Average plunged as many as 945 points before finishing with a loss of roughly 450, and the Nasdaq composite sank 1.6%. The combination of a weak economy and high inflation is a worst-case scenario for investors because the Federal Reserve has no good tool to fix both problems at the same time. On Friday: The S&P 500 fell 90.69 points, or 1.3%, to 6,740.02.