gwd math 6-28

lixiaoguangs

 

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)

ANS：D

 

 

我的解法：

R_a=P_a/[P_a+(1-P_a)*1.25]=P_a/[1.25-0.25P_a ]=4P_a/[5-P_a]=400P_a/[500-100P_a]%

我那里写错了吗？

lixiaoguangs

呀  没事了  %把我用浑了… 

lizhihuantu

这题我更郁闷，我做的时候把copies of Newspaper A 和 Newspaper A当成了2个东西，结果郁闷了至少7,8分钟。