新GRE考試技巧：數學重要考點AP
新gre考試實施以來，不僅對寫作部分茫然不知所措，就連我們所擅長的數學也甚是擔憂，相信這其中的`原因還是由於考生在新gre數學複習時沒有把基礎打牢。如果新版gre數學基本考點都沒有複習到，如何能拿到分數呢?所以說，想要新版gre數學考好，複習的時候一定要把基本概念和重要考點都弄紮實。 天針對新版gre數學複習，小編給大家整理的是關於平均數的相關內容，這些概念在考試中一定會考到的。希望考生能再接再厲，取得一個好成績，突破新版gre數學難的困境。
AP
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= 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.
由於美國數學基礎教育的難度增加導致數學考試越來越難，但新gre數學複習考點都是高中時候學到的知識點，考生不要過於緊張，把基本概念弄明白，再記住一些新版gre數學必備的詞彙，那麼相信新版gre數學應該沒有問題。
