Question

Find the HCF and LCM of 18 and 45 by prime factorisation method.

Answer 1

Express 18 and 45 as product of primes.
$18=2\times 3\times 3\times =2\times 3^2$
$45=3\times 3\times 5=3^2\times 5$
$\therefore$ HCF of $18$ and $45=3\times 3=9$
LCM of $18$ and $45=3\times 3\times 2\times 5=90$
Recall : HCF of any 2 positive integers is the product of the smallest power of each common prime factor of the numbers.
LCM of any 2 positive integers is the product of the greatest power of each factor of the numbers.