New York stock markets marked the anniversary of the worst market crash, dropping sharply Friday on a trade group report showing a drop in existing home sales. The National Association of Realtors said existing home sales dropped 1.7 percent in September from August, an indication a recovery in the housing market was still shaky. Friday was the 25th anniversary of Black Monday, Oct. 19, 1987, when markets crashed around the world. The Dow Jones industrial average dropped 508 points that day, 22.61 percent, to 1,738.74. Although the Dow has lost more points in a day several times since, that is the record for a one-day decline in the Dow in terms of percentage. After snapping a four-day winning streak Thursday, the Dow gave up 199.23 points or 1.47 percent to 13,349.71 in early afternoon trading. The Nasdaq composite index was down 64.85 points or 2.11 percent to 3,008.01. The Standard and Poor\'s 500 index lost 23.35 points or 1.6 percent to 1,433.99. The benchmark 10-year treasury note rose 18/32 to yield 1.772 percent. The euro fell to $1.3024 from Thursday\'s $1.3067. Against the yen, the dollar rose to 79.29 yen from 79.28 yen. In Japan, the Nikkei 225 index added 0.22 percent, 19.82 points, to 9,002.68. In London, the FTSE 100 index shed 0.35 percent, 20.90, to 5,896.15.