再问一道数学

jtcjxk

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 newspaper that day. If r percent of the store's revenues from newspaper sales was from A and if p percent of teh newspapers that the store sold were copies of newspaper B, which of the following expresses r in terms of p?

Answer is 400p/(500-p)

I have no idea how to get this. Could anyone give me a hint?

Thanks a lot!

 

kobexing

设总卖掉X，r/100=（x-px/100)/[x-px/100+1.25px/100]=(1-p/100)/(1+0.25p/100),r=(100-p)/(100+0.25p),我感觉答案有问题~