Last Sunday a certain store sold copies of Newspaper A for $1.00 each and copies of Newspaper B for $1.25 each, and the store sold no other newspapers that day. If r percent of the store’s revenues from newspaper sales was from Newspaper A and if p percent of the newspapers that the store sold were copies of newspaper A, which of the following expresses r in terms of p?
~$\frac{100p}{125-p}$~
~$\frac{150p}{250-p}$~
~$\frac{300p}{375-p}$~
~$\frac{400p}{500-p}$~
~$\frac{500p}{625-p}$~
根据题目可以设两个非常简单的式子:(r/100)*(A+1.25B)=A; (p/100)*(A+B)=A,但是这倆式子得不出结果,所以再列两个对应的式子:[(100-r)/100]*(A+1.25B)=1.25B; [(100-p0/100]*(A+B)=B.一除三,或二除四,就可以把AB比例找出来,再代入第一次算出来的式子,就可以约掉A或者B只剩下r和p了。
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