3道Prep

cathyyan

    

    

1)For every positive
even integer n, the function h(n) is defined to be the product of all the even
integers from 2 to n, inclusive.  If p is
the smallest prime factor of h(100) + 1, then p is

    

 

    

(A) between 2 and
10

    

(B) between 10 and
20

    

(C) between 20 and
30

    

(D) between 30 and
40

    

(E) greater than 40

answer: E

    

2. For a finite
sequence of nonzero numbers, the number of variations in sign is defined as the
number of pairs of consecutive terms of the sequence for which the product of
the two consecutive terms is negative. 
What is the number of variations in sign for the sequence 1, -3, 2, 5,
-4, -6 ?

    

 

    

(A) One

    

(B) Two

    

(C) Three

    

(D) Four

    

(E) Five

answer: C

    

In a stack of
boards at a lumber yard, the 20th board counting from the top of the stack is
immediately below the 16th board counting from the bottom of the stack.  How many boards are in the stack?

    

 

    

(A) 38

    

(B) 36

    

(C) 35

    

(D) 34

    

(E) 32

answer: D

charismale

1)看这里：

http://forum.chasedream.com/dispbbs.asp?boardID=22&ID=321064&page=1

2)问在一个固定顺序的序列里面，两个连续的数之积为负有几对。

这个固定顺序的序列为{1, -3, 2, 5, -4, -6}，则满足条件的有{1，-3}{-3，2}{5，-4}共三对，选择C

3)一堆东西叠起来，从上往下数的第20层below从下往上数的第16层，简图如下：

1

2

3

……

18

19  16

20  15

    14

    ……

    3

    2

    1

很容易得到总共有20+16-2=34层

cathyyan

Very clear, Tks