Chapter 9 - Basic Algebra - 9.2 Adding and Subtracting Signed Numbers - 9.2 Exercises - Page 638: 16

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To add $9+(-10)$, we can take the absolute value of both numbers. $|9|=9$ $|-10|=10$ Next, we can subtract the lesser absolute value from the greater absolute value. $10-9=1$ The number with the greater absolute value is negative, so the result will be negative. Therefore, $9+(-10)=-1$.