The importance of Working with Numbers has increased tremendously in all Aptitude based tests in the last few years. In CAT exam the number of questions asked have outgrown to 25%. Further Number System is the stepping stone for whole of the Quant, Data Sufficiency and Data Interpretation. The book "Koncepts of Numbers" captures Number System like never before. The book is an 100% original work by the author and contain some new copyrighted formula (not in public domain at present). With more than 1300 solved questions divided into 10 different chapters, it strengthens the basics and then further moves on to 5 difficulty levels of problems Concept Applicator (CA), Concept Builder (CB), Concept Cracker (CC), Concept Deviator (CD), Data Sufficiency (DS). The book has a 360 degree approach towards solving problems and having 20% of the total questions on Data Sufficiency. Students appearing for competitive exams like CAT, GMAT, XAT, IIFT, MAT etc. would find it extremely student friendly. It clears the ambigousness, and provides a vivid knowledge about the Number System. A musthave book for all aptitudebased exam takers. The book encapsulates Vedic Maths, Number Introduction, Factor Theory, HCF & LCM, Base System, Cyclicity, Remainders, Surds and Factorials. The books also covers past questions of various exams like, CAT, XAT, IIFT, SNAP, etc. Solutions, unlike other books where only hints are provided, are explained explicitly and elaboratively. About the Author: Mr. Gajendra Kumar has carved a niche for himself, being one of the best CAT/ GMAT trainers of Eastern India and popularly known as 'CAT Guru Gajen.' He is the FounderDirector of one of Kolkata's premier training institute. He has also to his credit 2 books written for CAT.