''an'' 80 % decreas
下記の文中で気になる箇所があったので質問させてください。
80 percent の前にある ''an'' はどいう意味をもっていますか。
As a result, there has been up to an 80 percent decrease in livestock losses and farmers have developed more tolerance for having cheetahs around.
--補足--
【出展】
http://www.voanews.com/english/news/usa/people/-US-Woman-Fights-to-Save-Cheetahs-123739294.html
【前後の文】
Over the past 15 years, CCF has donated more than 400 dogs to Namibian livestock farmers. As a result, there has been up to an 80 percent decrease in livestock losses and farmers have developed more tolerance for having cheetahs around.
Since the introduction of the guard dog program, CCF says the population of cheetahs in Namibia has risen from about 1,000 to 1,500, to between 3,500 and 4,000.
