麻烦来了！gwd-5- 25/ 28

25: If the number 52, 1n9, where n represents the tens digit, is a multiple of 3, then the value of n could be which of the following?

6,5,3,1,0

To me 52 has nothing to do with this question but why it's in? and could anybody know how to solve it?

28: 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 newpapers that the store sold were copies of newspaper A, which of the following expresses r in terms of p? below is my calculation :

1*(1-p)/1 (1-p)+1.25P=r ; am i right?

Q25:

5+2+1+n+9 should be the multiple of 3

so n can be 1

(na+nb)*p=na; (na*1+nb*1.25)*r=na*1

=>na(1-p)=nb*p; nb*1.25*r=na(1-r)

=>(1-p)*1.25*r=p*(1-r)

=>p/((1-p)*1.25+p)=r

没加%, 改过来了, 呵呵