I.25 Percentage decrease. On Monday, September 10, 2001 (the day before the September 11 attacks), the NASDAQ stock index closed the day at 1695. By the end of Monday, September 17, 2001 (the first full day of trading after the attacks), the NASDAQ stock index had dropped to 1580. By what percentage did the index drop? (Hint: See pages 191–194.)