涛涛数学一题，请问大牛，谢谢先

luqiao0709

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 B, 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，但我算出的是：4p/(5-p),不知错再哪，请大牛指点,谢谢

喝咖啡的狼

题干错了

mikecello

这道题完全可以算出答案的啊
p/(100-p)+1.25=100P/{r(100-p)}
算出来就是100p/(125-.25p)= 400p/(500-p)

将几个关系列出三个等式就可以求解了。
1.a+1.25b=X
2.rX=100a
3.a=p/(100-p) * b