Question:
What number should be added to $\frac{-5}{7}$ to get $\frac{-2}{3} ?$
Solution:
Let $x$ be added.
$\therefore x+\frac{-5}{7}=\frac{-2}{3}$
$\Rightarrow x=\frac{-2}{3}-\frac{-5}{7}$
$\Rightarrow x=\frac{-14}{21}-\frac{-15}{21}$
$\Rightarrow x=\frac{-14-(-15)}{21}$
$\Rightarrow x=\frac{-14+15}{21}$
$\Rightarrow x=\frac{1}{21}$