GRE数学增加了难度,不过,小编相信,我们中国的考生还是hold住的~~在这种情况下,了解数学词汇,端正数学基本概念和熟悉相应实例非常重要。来看下面这个系列吧。
排列组合
排列数公式和组合数公式:
排列:
组合:
乘法原理:
一件事的完成可以分成n个步骤,完成其第一步有m1种方法,完成第二步有m2种方法……完成第n步有mn种方法,那么完成这件事一共有N=m1*m2*……*mn种不同的方法。
例题.If all of the room numbers in a certain hotel must be even numbers, and if each of the numbers uses all four of the digits 3,4,5 and 8, what is the greatest number of four-digit numbers that the hotel can have?
例题.What is the total number of different 4-digit integers in which the units’ digit is an odd integer while the thousands’ digit is an even integer?
例题.What is the total number of different 5-digit numbers that contain all of the digits 1,2,3,4, and 5 and
1) in which none of the odd digits occur next to each other?
2) in which none of the even digits occur next to each other?