H.C.F. means Highest Common Factor Finding H.C.F. using Prime Factors Step I: Find the prime factorization of each of the given numbers. Step II: The product of all common prime factors is the HCF of the given numbers. Prime number is a number that is divisible only by itself and 1 (e.g. 2, 3, 5, 7, 11, 13,17 etc.) Applying the above to find the H.C.F of 18,36 and 60 Step I: 18=2×9=2×3×3=2×32 NOTE: a×a=a1×a1 From the law of indices, am×an=am+n Hence 3×3=31×31=31+1=32 36=18×2=2×3×3×2=2×2×3×3=22×32 60=2×30=2×2×15=2×2×3×5=22×3×5 Step II: The product of all common prime factors is 2×3