请教PREP数学，实在不解

cambycc

今天下午模考数学只有49，希望大家帮忙啊！

store s sold a total of 90 copies of a certain book during the seven days of last week,and it sold different numbers of copies on any two of the days,if for the seven days store s sold the greatest number of copies on Saturday and the second greatest number of copies on Friday,did store s sell more than 11 copies on Friday?
1,last week store s sold 8 copies of the book on Thursday.
2,Last week store s sold 38 copies of the book on Saturday.

statememt 2 alone is sufficient,but statement 1 alone is insufficient.

on jane's credit card account, the average daily balance for a 30-day billing cycle is the average(arithmetic mean) of the daily balances at the end of each of the 30days.At the beginning of a certain 30-day billing cycle, Jane's credit card account had a balance of $600. Jane made a payment of $300 on the account during the billing cycle. If no other amounts were added to or subtracted from the account during the billing cycle, what was the average daily balance on Jane's account for the billing cycle.
1,Jane's payment was credited on the 21st day of the billing cycle.
2, the average daily balance through the 25th day of the billing cycle was$540.

at a dinner party, 5people are to be seated around a circular table. two seating arragnements are considered different only when the positions of the people are different relative to each other. what is the total number of different possible seating arrangements for the group?
24???

of the 60 animals on a certain farm, 2/3 are either pigs or cows. how many of the animals are cows?
1, the farm has more than twice as many cows as it has pigs.
2, the farm has more than 12 pigs.
both.

冰凌雨

第一题：B

B：Sat最大，即38本，若Fri<= 11本，则我们可以取最大的11，那么剩余天数依次取最大值10 9 8 7 6，7天共89本，小于90本。

所以只有在Fri取大于11本时才可行！

A：其他天可以有很多方法满足90本的总条件

第四题，我也错过，不知

cambycc

麻烦大家帮忙解答啊，这几道我怎么看都不明比啊啊。

bruceala

第四题： cow+pig=40,同时，条件（1）cow大于2倍的pig，根据条件（2）pig大于12的话，当pig等于13时，满足 40 ，当pig=14的时候，则pig+cow将大于40，所以pig只能为13，则cow只能为27

candlelight

of the 60 animals on a certain farm, 2/3 are either pigs or cows. how many of the animals are cows?
1, the farm has more than twice as many cows as it has pigs.
2, the farm has more than 12 pigs.
both.

60 * (2/3) = 40

設牛為x, 豬為y , x + y = 40

(1) 牛是豬的2倍， x = 2y 將此式代入 x + y = 40 , 分別可得出(x , y) = (26,14)(28,12)... 多個組合，不唯一，不充份

(2)豬有12隻以上，單一條件不充份

(1)+(2) 可得唯一解 x = 27, y=13

[此贴子已经被作者于2008-8-10 0:48:58编辑过]

cambycc

那第三题呢？求高人指点啊！

candlelight

看到有一解法：

at a dinner party, 5people are to be seated around a circular table. two seating arragnements are considered different only when the positions of the people are different relative to each other. what is the total number of different possible seating arrangements for the group?
24???

5! / 5 = 24

但為啥除5 , 好像是因為重覆的關系.. (我也不太了解 除5的原因 )

但確定這個算法兒是對ㄉ

若版主知道為啥除5, 再貼上來吧..

cambycc

对啊，为什么除以5啊？

laipe0704

第三題  參考一下吧 http://www.stat.nuk.edu.tw/prost/content_new/c2-4.htm 有"環狀排列"的解釋 

dianecarton

信用卡签帐期那道好像还没有人说，选D

1）(600*20+300*10)/30

2)(540*25+300*5)/30