After delivering all of those presents, the elves were ready to eat some cookies. 50% of the cookies were sugar, and the rest were gingerbread. After eating 1,600 cookies, the number of sugar cookies decreased by 20% and the gingerbread cookies decreased by 60%. How many cookies did the elves have to start?
Clearly there were equal numbers of sugar and ginger cookies. So, if there were x of each to start with, and y sugar cookies were eaten, then
y = .20x
1600-y = .60x
Now just solve for x, and there were 2x cookies to start with