What two numbers have a GCF of 21?

Here we will explain and show you how to find what two numbers have the Greatest Common Factor (GCF) of 21.

There is actually an infinite number of answers to this question. First, note that both the numbers we are looking for must be multiples of 21. Below is the beginning list of multiples of 21 (1 through 7) in numerical order.

1. 21
2. 42
3. 63
4. 84
5. 105
6. 126
7. 147
etc...

Two numbers that have a GCF of 21 can be 21 and any other number on the list above. Thus, two numbers that have a GCF of 21 are:

21 & 42
21 & 63
21 & 84
etc...

That is not all! Any combination of any multiple of 21 and "odd" multiples of 21 will also have GCF of 21. We numbered the multiples above so it would be easy to identify the "odd" multiples (number 1, 3, 5, 7, etc). Thus, here are some more examples of two numbers that also have a GCF of 21.

42 & 63
42 & 105
84 & 105
84 & 147
etc...

Like we stated above, there are infinite combinations of two numbers whose GCF is 21. The lists we created can go on forever.

Two numbers have a GCF of Calculator
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Teacher Tip: If you are a teacher, you could ask these questions of your students: "I am thinking of two numbers and the GCF is 21, what are the numbers?" or "What are two numbers whose GCF is 21?"

What two numbers have a GCF of 22?
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