GMAT数学算术类题目中，整数概念、百分比和描述统计这三类题目所占比例稳居前三并在数值上远超其他类型的题目。今天我们就来说一下GMAT数学描述统计。
1. 算术平均数(Average or Arithmetic Mean)：所有数据之和除以数据个数;
2. 中数(Median)：将所有数据从小到大排列，取中间的数或中间两个数的算术平均数;
3. 众数(Mode)：一组数据中出现频率最高的数;一组数据中可能不止一个众数;
4. 极差(Range)：一组数据中最大数与最小数之差;
5. 方差(Variance)：一组数据中每个数与算术平均数之差的平方和的算术平均数;
6. 标准方差(Standard Deviation)：方差的平方根。
7. 频率分布(Frequency Distribution)
例题：OG13-P278-37The average (arithmetic mean) price of the 3 items that Kate purchased from a clothing store was $50. If there was no sales tax on any item that had a price of less than $80 and 6 percent sales tax on all other items, what was the total sales tax on the 3 items that Kate purchased?
(1) The price of the most expensive item that Kate purchased from the store was $100.
(2) The price of the least expensive item that Kate purchased from the store was $10.
A Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C BOTH statement TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D EACH statement ALONE is sufficient.
E Statements (1) and (2) TOGETHER are NOT sufficient.
解析：假设购买了a,b,c三件东西，假设其价格从低到高分别为a,b,c;其价格的均值为50，即(a+b+c)/3=50; 对(1)，c=100;因为对价值大于等于80元的东西要征6%的税，所以c要交税;因为a+b=50*3-100=50;a和b的价值总和都没有超过80，所以a,b都不用纳税;可得总税款为100*6%=6元;对(2)：(10+b+c)/3=50; b+c=140; 可能要交税，可能不要交税。
例题：OG16-P289-135Are all of the numbers in a certain list of 15 numbers equal?
(1) The sum of all the numbers in the list is 60.
(2) The sum of any 3 numbers in the list is 12.
A Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C BOTH statement TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D EACH statement ALONE is sufficient.
E Statements (1) and (2) TOGETHER are NOT sufficient.
解析：问这个list当中这15个数字是不是都相等?(1)15个数之和等于60不能保证15个数相等，可能性很多;(2)任意3个数字之和等于12，经试验只有当所有的数字都等于4时才能满足条件;所以选B。
》》点击了解GMAT数学的描述统计知识点
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