Probability theory and statistics

Abstract

Combinatorial analysis investigates the different possibilities for the arrangement of objects, for example, the questions: ‘How many ways are there of arranging four letters in a row?’, or ‘In how many different ways can five different numbers be selected from 90 numbers?’-The objects of the investigation can be, for instance, numbers, letters, persons, tests. They are called elements and are denoted by numerals or letters. If two arrangements do not contain the same elements, orr example, ab, cd, or if they do contain the same elements but not the same number of times for each, for example, aab, abb, then they are regarded as different. Arrangements such as aabb, abab fae regarded as different only if the ordering is taken into account.