倒晕了~~~~~~各位给倒倒吧~~谢谢啦

Avatar800 · 发表于 2010-6-30 21:47:39

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?

A.100p / (125 – p)
B.150p / (250 – p)
C.300p / (375 – p)
D.400p / (500 – p)

E.500p / (625 – p)
answer:d

mecsid · 发表于 2010-6-30 21:54:16

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?

A.100p / (125 – p)
B.150p / (250 – p)
C.300p / (375 – p)
D.400p / (500 – p)

E.500p / (625 – p)
answer:d

-- by 会员 Avatar800 (2010/6/30 21:47:39)

个人对此题表示无语之前貌似有贴讨论过

Avatar800 · 发表于 2010-6-30 22:06:46

倒一下吧~~帅哥~~我真没弄出来~

jackraywen · 发表于 2010-6-30 22:26:28

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 newspapers that the store sold were copies of newspaper A, which of the following expresses r in terms of p?

假设总共有M份newspapers were sold，两个条件得出两个式子，
P％*M＊1=R%*Revenues
P%*M＊1＋（1－P％）M＊1.25＝Revenues
＝＝＝＝＝＝＝》
P%*M＊1＋（1－P％）M＊1.25=(P%*M*1)/R%
==========>
P%+1.25-1.25*P%=P%/R%
==========>
R%=P%/(1.25-0.25*P%)
==========>
R%=P/{25(5-P%)}
==========>
把所有百分号都去掉就得到R＝400P／（500－P）了

passiona · 发表于 2010-6-30 22:28:57

total revue x, total newspaper y

A: revenue: p%y * 1.00 = r%x
B (1-p%)y * 1.25 = (1-r%)x

A/B: p/1.25(100-p)=r/(100-r)

Avatar800 · 发表于 2010-7-1 08:51:17

多谢了~~~~当时倒了半天也没弄对，真叫一个郁闷~

crazyxxx · 发表于 2010-7-1 10:02:13

推倒了一把,呵呵
发现这道题绝对是考细心的...

icyblue · 发表于 2010-7-1 10:21:43

考耐心！！

Avatar800 · 发表于 2010-7-1 13:07:54

哎~~这种题，考试遇到，一遍没弄对，肯定没心情再算一遍............

倒晕了~~~~各位给倒倒吧谢谢啦

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