Chapter 1 - Introduction to Algebraic Expressions - 1.5 Addition of Real Numbers - 1.5 Exercise Set - Page 42: 56

$-\frac{2}{9}$

To add two numbers with different signs, we subtract their absolute values ($\frac{1}{3} - \frac{1}{9} = \frac{3}{9} - \frac{1}{9} = \frac{2}{9}$) and take the sign of the larger absolute value, which is negative ($-\frac{2}{9}$).