What are the common multiples of 21 and 9?

Common multiples of 21 and 9 are numbers that both 21 and 9 can be divided into evenly with no remainder.

To find the common multiples of 21 and 9, we compare the list of multiples of 21 with the list of multiples of 9 to see what they have in common.

To create a list of multiples of 21, we multiply 21 by 1, 21 by 2, and so on like this:

21 x 1 = 21
21 x 2 = 42
21 x 3 = 63
21 x 4 = 84
...

Similarly, to create a list of multiples of 9, we multiply 9 by 1, 9 by 2, and so on like this:

9 x 1 = 9
9 x 2 = 18
9 x 3 = 27
9 x 4 = 36
...

When we compare the two lists to see what they have in common, we get the answer to "What are the common multiples of 21 and 9?"

63, 126, 189, 252, etc.

Since 63 is the first number they have in common, 63 is the least common multiple of 21 and 9.

Note: Our lists are shortened because they go on forever, but can you see the pattern when you look at the answer in green above? The common multiples are in intervals of 63 (the least common multiple), so you can continue the green list above with more common multiples of 21 and 9 by simply adding 63 to the last number on the list.

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What are the common multiples of 21 and 10?
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