PP- T1-PS48

[小花]

正確答案是粗體字

48. 6225-!-item-!-187;#058&004914
A certain city with a population of 132,000 is to be divided into 11 voting districts, and no district is to have a population that is more than 10 percent greater than the population of any other district. What is the minimum possible population that the least populated district could have?

(A) 10,700
(B) 10,800
(C) 10,900
(D) 11,000
(E) 11,100

65. 7870-!-item-!-187;#058&005675
For how many integers n is 2^n = n^2 ?

(A) None
(B) One
(C) Two(D) Three
(E) More than three

這一題我只有想到n=2
75. 8939-!-item-!-187;#058&006136
A certain law firm consists of 4 senior partners and 6 junior partners. How many different groups of 3 partners can be formed in which at least one member of the group is a senior partner? (Two groups are considered different if at least one group member is different.)

(A) 48
(B) 100
(C) 120
(D) 288
(E) 600
77. 9031-!-item-!-187;#058&006222
At a dinner party, 5 people are to be seated around a circular table. Two seating arrangements 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?

(A) 5
(B) 10
(C) 24
(D) 32
(E) 120
排列組合的觀念
我竟然算成10

[zacchen]

48.
X+1.1X*10=132000
12X=132000 X=11000

65.
2^4=4^2

75.
求出連一個senior都沒有的組合數是多少,用全部的組合數去減,就是答案
10C3- (6C3* 4C0)

77.
4p4

http://www.formosamba.com/phpBB3/viewtopic.php?t=893

[sgoo]

75.
當初在做75題時總會把他想成 4C1*9C2=144
從4個Senior選一個其餘9個在選兩個
為什麼錯呢？？

[zacchen]

[quote="sgoo"]75.
當初在做75題時總會把他想成 4C1*9C2=144
從4個Senior選一個其餘9個在選兩個
為什麼錯呢？？[/quote]

因為在你所說的"其餘九個"中包含了其他三個沒被選中的senior
也就是所從"三個senior跟六個junior中"選出兩個
變成了大雜燴了

另一個比較繞的方法
4C1*6C2+4C2*6C1+4C3*6C0
參考一下