A writing brush in the stationery department of a shopping mall, 25 yuan, and a calligraphy exercise book, 5 yuan. The shopping mall has formulated two preferential measures for promotion. Method a:

(2) from, solution:

Get，get:；

Get, get,

Therefore, when you buy less than 50 exercise books, paying by method A can save money; When you buy 50 exercise books, the two methods are the same; When you buy more than 50 exercise books, you can save money by paying by method B. ..

(1) (yuan) = total brush price +(x- 10) total exercise book price; (Yuan) = (total price of brush+total price of exercise book) ×0.9, which can be expressed according to these two equal relations;

(2) Just compare the relationship in (1) and pay attention to the discussion in different situations.