纠结了很久的一道PREP

xyqirene

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

tlyflying

觉得思路应该是这样的吧~~
if r percent of the store’s revenues from newspaper sales was from Newspaper A，
那么B报纸占总收入的比例就为1-r；
then， if p percent of the newspapers that the store sold were copies of newspaper A,那么B报纸所卖分数就占总报纸分数的1-P
再根据A,B报纸的单价，可列方程；P/1.25*(1-p)=r/(1-r)

xyqirene

。。是这样的··· 我读题的时候出错了···谢谢了