Finding HCF and LCM by Listing Method: For HCF, list all factors of each number and identify the largest shared factor. For LCM, list the multiples of each number and select the smallest shared multiple.

Prime Factorisation for HCF and LCM: For larger numbers, use prime factorisation. For HCF, take the lowest power of common prime factors; For LCM, take the highest power of all prime factors.