A: 25* 10=250 yuan 10 brush 10 exercise book.
b:25 * 90% * 10+5 * 90% * x = 225+4.5x。
(250-225)/4.5=5.55 In the second scheme, when purchasing 10 notebook, the price is 225+4.5* 10=270 yuan.
Therefore, when: ① the number of exercise books is less than or equal to 5, Scheme B is affordable.
② When the number of exercise books is more than 5, Scheme A is economical.