Prime Time

About this chapter

Prime Time is Chapter 5 of Class 6 Ganita Prakash and the chapter where number theory begins for the CTET aspirant. It introduces multiples and common multiples through the idli-vada game, then factors and divisors through Grumpy and Jumpy's treasure-hunting game. The chapter then defines prime numbers as numbers with exactly two factors (1 and the number itself) and composite numbers as those with more than two factors, with 1 belonging to neither. Students meet the Sieve of Eratosthenes as a method to list primes up to 100, study twin primes, learn co-prime pairs, and finally build the prime factorisation of a number using factor trees. Two applications follow — using prime factorisation to test whether two numbers are co-prime and whether one divides another. The chapter closes with divisibility rules for 10, 5, 2, 4 and 8. CTET Paper 2 routinely tests this chapter through prime/composite identification, factor-multiple problems, HCF/LCM through factorisation, and pedagogy items on the misconception that 1 is prime. The four tests below cover all six sections at the right depth.