gwd5-28, 做的很郁闷....

scorpio2rd

Q28:

Last Sunday a certain store sold copies of Newspaper A for $1.00 each and copies of Newspaper B for $1.25 each, and the store sold no other newspapers that day.  If r percent of the store’s revenues from newspaper sales was from Newspaper A and if p percent of the newspapers that the store sold were copies of newspaper A, which of the following expresses r in terms of p?

 

A.     100p / (125 – p)

B.     150p / (250 – p)

C.     300p / (375 – p)

D.     400p / (500 – p)

E.      500p / (625 – p)

答案是D

我怎么决的少条件呀.... 郁闷!!!! 可以解释如何做吗????

noooooofear

把题目化为等式: A/(A+1.25B)=r% 和A/(A+B)=p%. A,B表示售出的报纸数量