7. if |x|<.1? (老机经,不过条件1有变化) a) |x 1| <. 2|x-1| b) |x-3| <.>.0 (x<.>.3) 参考答案:E(原答案C) 思路:
8. A retailor bought 100 radios for $30 each, sold n radios for $50 each, and sold the left for x bucks each, made a total profit of $1500, then ask about whether x >. $40 or not? (老机经) (1) n >. 60 (2) n <. 80 参考答案:A 思路:50n (100-n)x=4500,x随n递减