Factors of 21 that add up to 18

We take "Factors of 21 that add up to 18" to mean "What combination(s) of two factors of 21 when added together will equal 18?"

We find the solution by first listing all the factors of 21 and then we find all the different combinations of two factors of 21 that when added together equal 18.

The factors of 21 are 1, 3, 7, and 21.

After trying all the different ways of adding the factors above together, we did not find any combinations of two factors of 21 that add up to 18.

However, one could argue that factors of 21 should include the negative counterparts to the positive factors above since minus times minus equals plus.

If we include the negative factors, we find the following combination(s) of two factors of 21 that add up to 18 to be as follows:

21 + (-3) = 18

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