# Find the H.C.F of 12, 15 and 21 using the prime factorisation method.

12 = 2 × 2 × 3

15 = 3 × 5

21 = 3 × 7

HCF = product of the smallest power of each common prime factor in the numbers = 3

3

12=2×2×3×

15=3×5

21=3×7

The HCF of a prime factors is =3

12=2×2×3

15=3×5

21=3×7

HCF=3

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