gre数学辅导：基本概念及实例解析(4)

会计考友

gre数学考试在新gre考试当中增加了一些难度，但是gre考生也不要太紧张，只要把一些gre数学基本概念掌握好，解题时就一定能轻松应对。  一元二次方程
ax2+bx+c=o
x12=[-b±(b2-4ac1/2)]/2a
9 d3 l3 d, ^0 z- [7 f( L* F5 v2 { 描述统计 Descriptive statistics
( u- ]5 k0 p6 ymode 众数
8 Z9 K7 M' r& G: U- Z一组数中出现频率最高的数
极差 range
; }) }4 f% P5 O一组数中最大值与最小值之间的差值
平均数 mean
7 l' d- I" f  B6 j) t; j4 R: k6 V7 x算术平均 arithmetic mean
! S( \5 C  J( j几何平均 geometric mean
例题.The circumference of a rectangle is 20
A.The greatest area of the rectangle
B.25
$ o# m) N1 R3 C; M5 ^9 s 中位数 median
, X$ t" \% s3 B- O; O中位数的寻找方法：
1.将所有n个数字按着从大到小或者从小到大排列；
2.如果n=奇，整个序列中位于中间位置的数就是中位数；如果n=偶，中间两个数的算术平均即是中位数。
例题.If the arithmetic mean of a, b, c, 3 and 5 is 6, which of the following must be true?
( v0 v* ^3 h. [0 `: @1.The median of the five numbers cannot be 3
! k7 Q1 v) R5 f' M7 _) k' g5 H# N2.At least one of a, b and c is greater than 7
3.The range of the five numbers is 2 or more
: Q5 I. z" v7 b- ?" vA.1 only
B.2 only
9 b! K. c5 [/ bC.3 only
0 [9 `$ ?. }: J3 P8 H& FD.1 and 3
  ]8 V( ]4 l# @/ g0 d  g  `E.2 and 3
: \6 O7 i; E( ? 例题.A group of students were tested on data-entry skills, and the number of errors they made and the percent of students making x errors were recorded as follows.
Number of errors
" g+ N9 S, O  n1 A8 j: B$ LPercent of students
$ v; [+ u9 a: A8 i0
1%
1
$ X( G8 E; G$ z- _% e2 O9 l( f7%
3 D1 x/ G  C' I* ]2
2 b4 n; Y) T( F/ z6 i  p& ~8%
% h/ B  O2 |' k, A* q1 _/ C/ S3
25%
' @0 X& B# i0 K6 q4
19%
5
18%
6 or more
: p8 B% k  r! q! ?) ^22%
9 V; ^& W: n, C: m" f& n# E7 c  J
1. What is the range for the number of errors made by the students in the sample?
& u' e; U1 G! I5 R  G6 IA. 4
B.5
0 h; e- Q5 Y: b, L8 j$ OC.6
% v& ?" s' ~- D3 @1 B) uD.7
E. It cannot be determined from the information given.
2. What was the median number of errors in the sample?
+ s& E1 J: f% k  Q; n% FA.3
B.3.5
6 D) y5 `( ~* L/ k( J! NC.4
D.4.5
E. It cannot be determined from the information given.
          平时，gre考生一定要注意gre数学基本概念的加强理解，因为无论gre数学考试怎样的题目都是从最基本的概念中演变而来的。