7月JJ 216

soul86

216  during
the last year the range of one stock's closing price is r, six weeks ago the
closing price of the stock is p, yesterday the closing price of the stock is x,
which of the following can be x in term of p and r? (A) p-2r, (B) p-0.5r        (C)p+3r   (D) p+4r  
答案 B，
        放缩法：
        不妨设平均数为m，则有
m-0.5r<=x<=m+0.5r, 
m-0.5r<=p<=m+0.5r,          推出  p-0.5r<=m=p+0.5r
推出  p-r<=x<=p+r, 所以选B

    

Guang722(&
chen): 选B。只有B才表示股票价格有可能没有超出range。

    

时间：上一年的范围是r，六周前是p，昨天是x，那么x应该在r的值域当中，因此，p-0.5r<=x<=p+0.5r

这题不大懂，谁能帮忙解答下，谢谢

soul86

顶上去~