8.24请教几道PS题

liptontea · 发表于 2010-8-24 15:31:03

1. Of the science books in a certain supply room, 50 are on botany, 65 are on zoology, 90 are on physics, 50 are on geology, and 110 are on chemistry. If science books are removed from the supply room, how many must be removed to ensure that 80 of the books removed are on the same science?
A. 81
B. 159
C. 166
D. 285
E. 324

2. If n is a postive integer, what is the remainder when 3^(8n+3) + 2 (3的8n+3次方）is divided by 5?
A. 0
B. 1
C. 2
D. 3
E. 4

3. A certain company assigns employees to offices in such a way that some of the offices can be empty and more than one employee can be assigned to an office. In how many ways can the company assign 3 employees to 2 different offices?
A. 5
B. 6
C. 7
D. 8
E. 9

they keys: 1 E, 2 A, 3 D

多谢解答！

gaor · 发表于 2010-8-24 15:59:39

第一题问取出的书中有80本是同一课题
50 are on botany, 65 are on zoology, 50 are on geology 都不满足，所以先把这些取出来
90 are on physics, and 110 are on chemistry 满足但有可能某一科只取出79本，所以把这个也算进去

50+65+50+79+80 = 324

liptontea · 发表于 2010-8-24 22:36:29

多谢解答！能否解答下后面二题？Thanks very much!

gaor · 发表于 2010-8-25 15:08:13

第二题我算出来选b
3的8n+3次方 + 2 乘以 3的8n+3次方 => 3的4(2n+1)次方，所以末尾应该是1，除以5的话余数是1

不知道其他人怎么想这道题

gaor · 发表于 2010-8-25 15:12:39

第三题一开始不确定，后来认为题目的意思是说：3个员工，2个办公室，允许这两个办公室中的一个是空的

一个办公室1个人另一间2人有6种情况
还有2种情况是3个人在同一间办公室

andreasyang · 发表于 2010-8-25 15:50:03

第二题是E

alex318 · 发表于 2010-8-25 16:27:48

第二题是E

-- by 会员 andreasyang (2010/8/25 15:50:03)

同意，第二题是E,应为3的次方的结果个位是有规律的，一次是3^1个位是3， 3^2个位是9，3^3个位是7，3^4个位是1，然后循环下去，3^(8n+3)的个位应该和3^3个位相同，因为8n+3被4除余3，所以3^（8n+3) + 2的个位应该是7+2=9，所以被5除后余4.

gaor · 发表于 2010-8-25 17:04:58

liptontea 能不能把第二题题目重新贴一下

问题是 ‘3的8n+3次方 + 2 乘以 3的8n+3次方’？还是 ‘3的8n+3次方 + 2‘？
我认为两个答案应该分别是 B 和 E

liptontea · 发表于 2010-8-25 23:53:01

谢谢各位的解答！

第二题原文如下，括号中内容是我写的说明可能舞蹈大家了。
2. If n is a postive integer, what is the remainder when 3^(8n+3) + 2 is divided by 5?
A. 0
B. 1
C. 2
D. 3
E. 4

8.24请教几道PS题

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