7th Class Mathematics Related to Competitive Exam NUMBER & RANKING

Learning Objectives

• To understand ranking in a given set of items.
• To learn how a complex information can be simplified by ranking.

INTRODUCTION

A ranking is a relationship between a set of items such that, for any two items, the first is either 'ranked higher than', "ranked lower than" or 'ranked equal to' the second. In mathematics, this is known as weak order or total pre order of objects. It is not necessarily a total order of objects because two different objects can have the same ranking. The rankings themselves are totally ordered. For example, materials are totally pre ordered. For example, materials are totally pre ordered by hardness, while degrees of hardness are totally ordered. By reducing detailed measures to a sequence of ordinal numbers, ranking makes it possible to evaluate complex information according to criteria. For example, an internet search engine may rank the pages it finds according to an estimate of their relevance making it possible for the users to quickly select the pages they are likely to want to see.

Numbers and ranking is a type of Verbal Aptitude which judges quantitative aptitude of a student.

Example 1:

In a class of 60 where the number of boys are twice that of girls, Ramya ranked 17th from the top. If there are 9 boys ahead to Ramya, how many girls are after her in the rank?

(a) 26                     (b) 12                 

(c) 10                    (d) 33

Solution:

(b) There are 2 boys and 1 girl out of three.

\[\therefore \] Out of 60 there are 40 boys and 20 girls

Girls ahead of Ramya in rank = 16 – 9 = 7

Girls behind Ramya in rank =19 – 7 = 12