The price of each brush in the stationery department of a shopping mall is 25 yuan, and the price of each calligraphy exercise book is 5 yuan. Shopping malls have formulated the following two preferential promotion methods: the first one
Judging from the meaning of the question, the analytical formula of the first method is y1= 25×10+5 (x-10) = 200+5x.
The second analytical formula is Y2 = 25× 0.9×10+4.5x (x ≥10).
Solve equation 200+5x=225+4.5x,
D: x=50，
∴ When x < 50, y 1 < y2, adopt the first scheme;
When x=50, y 1=y2 can be used in two schemes;
When x > 50, Y 1 > Y 2 adopts the second scheme.