HCF (Highest Common Factor) can be found using the Euclidean algorithm. Calculation: Step 1: Find the HCF of 153 and 117 153=117×1+36 117=36×3+9 36=9×4+0 ⇒HCF(153,117)=9 Step 2: Find the HCF of the result from step 1 and 405 405=9×45+0 ⇒HCF(9,405)=9