新版GRE数学复习重要考点:Sum of Arithmetic ProGREssion
The sum of n-numbers of an arithmetic proGREssion is given by
S=nxdn/2
where x is the first number and d is the constant increment.
example:
sum of first 10 positive odd numbers:101+2109/2=10+90=100
sum of first 10 multiples of 7 starting at 7: 107+7109/2=70+315=385
remember:
For a descending AP the constant difference is negative.
由于美国数学基础教育的难度增加导致数学考试越来越难,但新GRE数学复习考点都是高中时候学到的知识点,考生不要过于紧张,把基本概念弄明白,再记住一些新版GRE数学必备的词汇,那么相信新版GRE数学应该没有问题。
AP
Average of n numbers of arithmetic proGREssion is the average of the smallest and the largest number of them. The average of m number can also be written as x + d/2.
Example:
The average of all integers from 1 to 5 is /2=3
The average of all odd numbers from 3 to 3135 is /2=1569
The average of all multiples of 7 from 14 to 126 is /2=70
remember:
Make sure no number is missing in the middle.
With more numbers, average of an ascending AP increases.
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