请教数学题一道

Q17:

Last year the price per share of Stock X increased by k percent and the earnings per share of Stock X increased by m percent, where k is greater than m.  By what percent did the ratio of price per share to earnings per share increase, in terms of k and m?

A.     k/m %

B.     (k – m) %

C.     [100(k – m)] / (100 + k) %

D.     [100(k – m)] / (100 + m) %

E.      [100(k – m)] / (100 + k + m) %

选d.

设原来的price是a,earning是b。那么现在的price就是a(1+k/100),现在的earning是b(1+m/100).

ratio的增加是a(1+k/100)/b(1+m/100)-a/b,在把所得结果除以a/b，然后就得出答案了。