GCF and LCM of 15 and 60 ( Least common multiple and Greatest common fac...

Thursday, November 1, 2018




What is the least common multiple and greatest common factor of the numbers 15 and 30?

The LCM of 15 and 60 = 60
The GCF of 15 and 30 = 15

I like to find the LCM and GCF by using a factor tree. A factor tree allows you to find all of the prime numbers of any numbers.
Once you know the prime numbers you can find both the least common multiple and greatest common factor.

Prime numbers of 15    3  5
Prime numbers of 60    2   2   3  5

Now for the LCM multiply all of the prime numbers together. If both numbers have the same number only multiply this number once.
3 x 5 x 2 x 2 = 60

For the GCF you multiply the prime numbers found in both sets of numbers

3 x 5


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