两题数学求解析

lizadlee

1，In a retail store,the average(arithmetic mean)sale for month M was d dollars.Was the average(arithmetic mean) sale for monthe J at least 20% higher than that for month M?
(1)For month M, total revenue from sales was $3500.
(2)For month J,total revenue from sales was $6000.
选E, 解析说题目中没有说明销售总收入与平均销售之间的换算关系，这两之间除了每月30天平均，还有啥换算关系啊？

2，Town T has 20,000 residents, 60% of whom are female. what percent of the residents were born in Town T?
(1) The number of female residents who were born in Town T is twice the number of male residents who were not born in Town T.
(2)The number of female residents who were not born in Town T is twice the number of male residents who were born in Town T.
选C, 不理解。

求解析。谢谢！！

Koothrappali

1、比如平均每个柜台的销量？

2、列方程
fb:female born;  fn:female not born; mb:male born; mn:male not born;

fb+fn+mb+mn=20000
fb+fn=12000
fb=2mn
fn=2mb

所以应该是可解的。

数学，一定要动笔算的！DS题不需要算出结果，但是式子还是需要列的，不动笔只想的话脑子会乱掉的……

lizadlee

1、比如平均每个柜台的销量？

2、列方程
fb:female born;  fn:female not born; mb:male born; mn:male not born;

fb+fn+mb+mn=20000
fb+fn=12000
fb=2mn
fn=2mb

所以应该是可解的。

数学，一定要动笔算的！DS题不需要算出结果，但是式子还是需要列的，不动笔只想的话脑子会乱掉的……

-- by 会员 Koothrappali (2012/11/13 23:32:18)

就是因为用笔算所以混乱了。。。
按你的设法，fb+fn+mb+mn=20000， fb+fn=12000，得出mn+mb=8000.
但根据fb=2mn，fn=2mb，可得 fb+fn=2mn+2mb=16000，
前后矛盾啊。。。。

krusher

第二题解不了

Koothrappali

1、比如平均每个柜台的销量？

2、列方程
fb:female born;  fn:female not born; mb:male born; mn:male not born;

fb+fn+mb+mn=20000
fb+fn=12000
fb=2mn
fn=2mb

所以应该是可解的。

数学，一定要动笔算的！DS题不需要算出结果，但是式子还是需要列的，不动笔只想的话脑子会乱掉的……

-- by 会员 Koothrappali (2012/11/13 23:32:18)

就是因为用笔算所以混乱了。。。
按你的设法，fb+fn+mb+mn=20000， fb+fn=12000，得出mn+mb=8000.
但根据fb=2mn，fn=2mb，可得 fb+fn=2mn+2mb=16000，
前后矛盾啊。。。。

-- by 会员 lizadlee (2012/11/13 23:57:18)

抱歉，我昨晚脑残了……

题干如果是这样的话就无解了，我百度了一下，发现一道几乎一样的题：
http://wenku.baidu.com/view/2736787302768e9951e7383e.html
第21题，条件二的题干是The number of female residents who were not born in Town T is twice the number of female residents who were born in Town T.

这样的话，
fb+fn+mb+mn=20000
fb+fn=12000
fb=2mn
fn=2fb

fn=8000，fb=4000，mn=2000，mb=6000，（fb+mb）/20000=50%


昨天晚上犯了懒，其实再推一步就能发现自己的错误了……再次抱歉！

lizadlee

1、比如平均每个柜台的销量？

2、列方程
fb:female born;  fn:female not born; mb:male born; mn:male not born;

fb+fn+mb+mn=20000
fb+fn=12000
fb=2mn
fn=2mb

所以应该是可解的。

数学，一定要动笔算的！DS题不需要算出结果，但是式子还是需要列的，不动笔只想的话脑子会乱掉的……

-- by 会员 Koothrappali (2012/11/13 23:32:18)

就是因为用笔算所以混乱了。。。
按你的设法，fb+fn+mb+mn=20000， fb+fn=12000，得出mn+mb=8000.
但根据fb=2mn，fn=2mb，可得 fb+fn=2mn+2mb=16000，
前后矛盾啊。。。。

-- by 会员 lizadlee (2012/11/13 23:57:18)

抱歉，我昨晚脑残了……

题干如果是这样的话就无解了，我百度了一下，发现一道几乎一样的题：
http://wenku.baidu.com/view/2736787302768e9951e7383e.html
第21题，条件二的题干是The number of female residents who were not born in Town T is twice the number of female residents who were born in Town T.

这样的话，
fb+fn+mb+mn=20000
fb+fn=12000
fb=2mn
fn=2fb

fn=8000，fb=4000，mn=2000，mb=6000，（fb+mb）/20000=50%


昨天晚上犯了懒，其实再推一步就能发现自己的错误了……再次抱歉！

-- by 会员 Koothrappali (2012/11/14 11:19:00)

MERCI BEAUCOUP!!!