What is the sum of 9 and 9?

What does it mean when someone asks you for the sum of 9 and 9? The sum is part of the addition equation displayed below.

addend + addend = sum

When someone asks "What is the sum of 9 and 9?" they mean that 9 is an addend and 9 is an addend in an addition equation.

Therefore, as you may have inferred, the sum of 9 and 9 is the same as 9 plus 9. Here is the addition equation with the answer:

9 + 9 = 18

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What is the sum of 9 and 10?
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