TT MATH5-28 求助各位

kimpossible

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)


题目看的我很混乱 而且算不出来。。。

ruochen

假设A报纸卖了a份，B报纸卖了b份
那么LAST SUNDAY的总收入就是a+1.25b
根据题目的意思有
0.01r(a+1.25b)=a
b=0.01p(a+b)

lipsilon

假设x, y是A和B卖出去的份数。y/(x+y) = p. 总的收入为M = x*1 + y*1.25, x/M=r/100.
r = 100*x / (x+1.25y) ........(1)
y= px/(1-p)              .........(2)
由以上两个方程可以得到 r 的值，因为x约去了。