The Singing Hedgehog Guide to:
Prime Factors 6 - Finding the HCF
If we have two or more numbers, expressed as the product of their prime factors, we can easily find the Highest Common Factor [the largest number that divides into all the values].

All we do is multiply together every factor that is common to all the values.

    Example:    Find the HCF of 24, 42 and 60

    24 = 2 x 2 x 2 x 3
    42 = 2 x 3 x 7
    60 = 2 x 2 x 3 x 5

    The factors common to all three are 2 and 3 so the HCF is 6.

    Harder Example: Find the HCF of 180, 420, 600.

    180 = 2 x 2 x 3 x 3 x 5
    420 = 2 x 2 x 3 x 5 x 7
    600 = 2 x 2 x 2 x 3 x 5 x 5

The common factors are 2, 2, 3 and 5 so the HCF is 60.
   
         Prime Factors        Cancelling fractions

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