大大解救math题啊！！

finger1234

1.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?

Key:400p/(500-p)  我怎么也算不到这个答案
2. A school administrator will assign each student in a group of n students to on e of m classrooms. If 3<m<13<n, is it possible to assign each of the n students to one of the m classrooms so that each classroom has the the smae number of students assinged to it?

(1) It is possible to assign each of 3n students to one of m classroom s so that each classroom has the same number of students assigned to it.

(2) It is possible to assign each of 13n students to one of m classroom s so that each classroom has the same number of students assigned to it.

Key:B why? What is that mean?
3. If the probability is 0.54 that Stock A will increase in value during the next month and the probability is 0.68 that Stock B will increase in value during the next month, what is the greatest possible value for the probability that neither of these two events will occur?

Key:0.32     为什么不是1-0.54*0.68  neither的意思不是两个都不会发生吗?

sanssouci

3。画个图会一目了然。

	A	non-A	Total
B	0.54	0.14	0.68
non-B	0	0.32	0.32
Total	0.54	0.46	1

highlight 的地方最多只能是0.32。