1
CHAPTER AT A GLANCE
The World of Numbers
•Unit: Number Systems
•Board weightage: Number Systems carries about 10 marks out of 80 in Class 9 (please check the latest sample paper)
•Key ideas from the textbook: integers and Brahmagupta's rules, rational numbers and their operations, density, irrational numbers, proof that √2 is irrational, decimal expansions, converting repeating decimals to fractions, cyclic numbers
•Proof asked: irrationality of √2 by contradiction
•Time to revise: about 60 minutes
1 of 8