The price of each brush of Xinhua Stationery is 25 yuan, and the price of each calligraphy exercise book is 5 yuan. Stationery stores have formulated two preferential measures to promote sales. A: Buy

The price of each brush of Xinhua Stationery is 25 yuan, and the price of each calligraphy exercise book is 5 yuan. Stationery stores have formulated two preferential measures to promote sales. A: Buy. (1) If you buy a brush, you get a calligraphy exercise book, which is equivalent to a brush 20 yuan and a calligraphy exercise book 5 yuan, so Y A =20× 10+5x=200+5x.

(2)y B =(25× 10+5x)×0.9 = 225+4.5x

(3)YA-YB =(200+5x)-(225+4.5x)= 0.5x-25。

When 0.5x-25 < 0, that is, when X < 50, Y A < Y B, so when X < 50, it is more economical to choose the priority method of A;

When 0.5x-25=0, that is, when x=50, Y A =y B, so when x=50, both parties pay in the same way;

When 0.5x-25 > 0, that is, when X > 50, Y A > Y B, so when X > 50, it is more economical to choose the second priority.