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Greatest Common Factors & Least Common Multiples
Overview
We can use what we know about multiplication to find the greatest common factor
(GCF) for a set of numbers. For example:
Find the greatest common factor of 21 and 7.
To find GCF, we need to look at the factors for each number. Factors are numbers
we can multiply together to get other numbers.
We can also use multiplication to find the least common multiple (LCM) of a set of
numbers. For example:
Find the least common multiple of 3 and 4.
To find the LCM, we need to look at the multiples of both numbers. Multiples are
repeated groups of the same amount.
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Find the greatest common factor of 10 and 30.
Answer
10
The factors of 10 are 1, 2, 5, and 10. The factors of 30 are 1, 2, 3, 5, 6, 10, 15 and 30.
Find the greatest common factor of 25 and 50.
Answer
25
The factors of 10 are 1, 2, 5, and 10. The factors of 30 are 1, 2, 3, 5, 6, 10, 15 and 30.
Find the greatest common factor of 18 and 30.
Answer
6
The factors of 18 are 1, 2, 3, 6, 9 and 18. The factors of 30 are 1, 2, 3, 5, 6, 10, 15 and 30.
Find the greatest common factor of 16 and 12.
Answer
4
The factors of 16 are 1, 2, 4, 8 and 16. The factors of 12 are 1, 2, 3, 4, 6, and 12.
Find the greatest common factor of 15 and 45.
Answer
15
The factors of 15 are 1, 3, 5, and 15. The factors of 45 are 1, 3, 5, 9, 15, and 45.
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