GMAT考试必看数学算数知识点：排列

对于GMAT考试的数学部分的备考来说，同学们需要通过大量的真题练习才能夯实基础，不断的掌握知识点以及一些难题的解题方法小编在坦途网GAMT考试频道还有很多相关的内容和考试资讯，下面就是小编为大家整理的详细内容，供大家参考！

There are some useful methods for counting objects and sets of objects without actually listing the elements to be counted. The following principle of Multiplication is fundamental to these methods.

If a first object may be chosen in m ways and a second object may be chosen in n ways, then there are mn ways of choosing both objects.

As an example, suppose the objects are items on a menu. If a meal consists of one entree and one dessert and there are 5 entrees and 3 desserts on the menu, then 5×3 = 15 different meals can be ordered from the menu. As another example, each time a coin is flipped, there are two possible outcomes, heads and tails. If an experiment consists of 8 consecutive coin flips, the experiment has 28 possible outcomes, where each of these outcomes is a list of heads and tails in some order.

☆阶乘：factorial notation

假如一个大于1的整数n，计算n的阶乘被表示为n!，被定义为从1至n所有整数的乘积，

例如：4! = 4×3×2×1= 24

注意：0! = 1! = 1

☆排列：permutations

The factorial is useful for counting the number of ways that a set of objects can be ordered. If a set of n objects is to be ordered from 1st to nth, there are n choices for the 1st object, n-1 choices for the 2nd object, n-2 choices for the 3rd object, and so on, until there is only 1 choice for the nth object. Thus, by the multiplication principle, the number of ways of ordering the n objects is

n (n-1) (n-2)…( 3) (2) (1) = n!

For example, the number of ways of ordering the letters A, B, and C is 3!, or 6：ABC, ACB, BAC, BCA, CAB, and CBA.

These orderings are called the permutations of the letters A, B, and C.也可以用P 33表示.

Pkn = n!/ (n-k)!

例如：1, 2, 3, 4, 5这5个数字构成不同的5位数的总数为5! = 120

相信考生们经过长期努力的练习，一定可以在很大程度上提高自己的考试成绩。所以这篇文章是非常有参考价值的，赶紧收藏吧！小编还会在网站更新一些关于GMAT考试模拟题，希望能够帮助大家备考，想要优质的备考资料，记着到坦途网哦！