Fortune Brands, Inc., sells a variety of products including Titleist and Pinnacle golf balls, Footjoy golf shoes, and Master Lock padlocks. Like many other companies, Fortune Brands reported a drop in net sales from $7.6 billion in 2008 to $6.7 billion in 2009, and a drop in gross profit from $3.6 billion in 2008 to $3.5 billion in 2009. Based on these numbers, determine whether the drop in gross profit was caused by a decline in gross profit per sale, a decline in sales volume, or a combination of the two.