The expression $-10 + (-3)$ can be simplified by adding the two negative numbers together:

$-10 + (-3) = -13$

So, $-10 + (-3) = -13$.

Would you like more details or have any questions?

Here are 5 related questions for practice:

1. What is $-5 + (-7)$?
2. Simplify $-20 + (-15)$.
3. What is the result of $-4 + (-9)$?
4. Evaluate $-8 + (-6)$.
5. Solve $-12 + (-8)$.

Tip: When adding two negative numbers, the result will always be negative. You just add their absolute values and keep the negative sign.