A GCF is the greatest number that two or more numbers have in common.
Example: The common factors of 15, 30 and 105<span><span>Factors of 15 are <span>1, 3, 5, </span>and<span> 15
</span></span><span>Factors of 30 are <span>1, 2, 3, 5, 6, 10, 15 </span>and<span> 30
</span></span><span>Factors of 105 are <span>1, 3, 5, 7, 15, 21, 35 </span>and<span> 105</span></span></span>
The factors that are common to all three numbers are 1, 3, 5 and 15
In other words, the common factors of 15, 30 and 105 are 1, 3, 5 and <span>15. The greatest being 15.</span>
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<span>D is the answer. The least common multiple of 10 and 20 is 20, not 40</span>