You'd better make a picture first to do this problem. The drawing method is to draw a 5-cell line segment to represent the number of fashions purchased by A. Obviously, the six cells in the drawing represent the number of fashions purchased by B. Because B sells at a profit of 50% and all of them are sold out, it means that B's total profit is 50% of the purchase amount. Net profit is 3 grids. If you convert the total price of B into the amount of fashion, you can buy 9 pieces of fashion. But A is sold at a price of 80% profit, which means that A's total profit is 80% of the purchase amount, and its net profit is 4 squares. If the total price of a is converted into buying fashion, it is also 9 squares. In this way, it is not difficult for us to see that A originally bought 5 batteries, and now it has added 4 batteries; And B originally bought 6 communities, and now it has added 3 communities. A has one more cell than B. This cell is exactly 10 sets of fashion that A earns more than B. Therefore, A originally bought 50 sets of this fashion.