# gre数学”算数“基础要牢靠

2020-01-11 19:03 来源：未知

准备gre数学我们一定要在gre数学复习中把基础打牢靠，什么才是gre数学的基础呢?比如gre数学公式是大家一定要熟记于心的，小编下面为大家分享一些关于算数的gre数学考点知识，供大家参考，希望可以帮助大家提高gre数学成绩。

GRE数学相当于中国高中数学的水平，对我国考生来说没有太大的问题，考生需要做得是不断巩固数学和语言基础，以防在最简单的部分出错。小编下面为大家分享一下关于算数方面的gre数学考点，希望对您gre数学复习有所帮助。

1.Sum of Arithmetic Progression(等差数列求和)

The sum of n-numbers of an arithmetic progression is given by

S=nx*dn(n-1)/2

where x is the first number and d is the constant increment.

example:

sum of first 10 positive odd numbers:10*1+2*10*9/2=10+90=100

sum of first 10 multiples of 7 starting at 7： 10*7+7*10*9/2=70+315=385

remember:

For a descending AP the constant difference is negative.

2.AP(等差数列求平均数)

Average of n numbers of arithmetic progression (AP) is the average of the smallest and the largest number of them. The average of m number can also be written as x + d(m-1)/2.

Example:

The average of all integers from 1 to 5 is (1+5)/2=3

The average of all odd numbers from 3 to 3135 is (3+3135)/2=1569

The average of all multiples of 7 from 14 to 126 is (14+126)/2=70

remember:

Make sure no number is missing in the middle.

With more numbers, average of an ascending AP increases.

With more numbers, average of a descending AP decreases.

AP:numbers from sum

given the sum s of m numbers of an AP with constant increment d, the numbers in the set can be calculated as follows:

the first number x = s/m - d(m-1)/2,and the n-th number is s/m + d(2n-m-1)/2.

Example:

if the sum of 7 consecutive even numbers is 70, then the first number x = 70/7 - 2(7-1)/2 = 10 - 6 = 4.

the last number (n=m=7)is 70/7+2(2*7-7-1)/2=10+6=16.the set is the even numbers from 4 to 16.

Remember:

given the first number x, it is easy to calculate other numbers using the formula for n-th number: x+(n-1)

AP:numbers from average

all m numbers of an AP can be calculated from the average. the first number x = c-d(m-1)/2， and the n-th number is c+d(2n-m-1)/2, where c is the average of m numbers.

Example:

if the average of 15 consecutive integers is 20, then the first number x=20-1*(15-1)/2=20-7=13 and the last number (n=m=15) is 20+1*(2*15-15-1)/2=20+7=27.

if the average of 33 consecutive odd numbers is 67, then the first number x=67-2*(33-1)/2=67-32=35 and the last number (n=m=33) is 67+2*(2*33-33-1)/2=67+32=99.

Remember:

sum of the m numbers is c*m,where c is the average.

3.Sequence of Numbers(序列)

A sequence is a set of numbers that follow a fixed pattern.The fixed pattern can be expressed by an equation or by a property.

Example:

A set of consecutive integers: 1,2,3,4,5(Fixed gap)

A set of consecutive even numbers:4,6,8,10,12 (Fixed gap)

A set of consecutive prime: 2,3,5,7,11(Fixed gap)

A set of consecutive power of 2:4,8,16,32,64(Fixed gap)

Remember:

A sequence can be in ascending or descending order.

上面的信息就是小编为大家介绍的一些关于算数的gre数学考点，大家在gre数学复习中可以参考学习下，希望对您提高gre数学成绩有所帮助，大家更多信息请关注留学，有问题可以咨询在线顾问老师，我们竭诚为您解答。

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