CBSE · Class 6-12

Class 6 · Ganita Prakash

Unit 5 · Class 6Ganita Prakash

Prime Time

Factors, multiples, primes, composites, HCF and LCM.

Lessons

4 concepts

1
Prime Numbers
Two factors only: $1$ and itself. First primes: $2,3,5,7,11,13,17,19,\ldots$ . Only even prime is $2$ . Sieve of Eratosthenes lists primes up to $N$ .
2
Prime Factorisation
Every composite $=$ product of primes uniquely. $84 = 2^2\cdot 3\cdot 7$ . Divide by smallest prime repeatedly.
3
Finding HCF
Take common primes to lowest power. HCF $(24,36)=2^2\cdot 3=12$ . Or use Euclid's division method.
4
Finding LCM
Take all primes to highest power. LCM $(24,36)=2^3\cdot 3^2=72$ .

Skills to practise

Skill · medium

Prime Time — Practice