Math worksheet for practicing addition and subtraction of negative numbers.

Problem: Adding and Subtracting Negative Numbers

The task involves solving a series of arithmetic problems involving addition and subtraction of positive and negative numbers. Below is the step-by-step solution for each problem, along with explanations.

---

#### 1. (-4) + (-5) =
- Adding two negative numbers results in a larger negative number.
- $ -4 + (-5) = -4 - 5 = -9 $
- Answer: $ \boxed{-9} $

---

#### 2. 8 + (-12) =
- Adding a negative number is the same as subtracting its positive counterpart.
- $ 8 + (-12) = 8 - 12 = -4 $
- Answer: $ \boxed{-4} $

---

#### 3. (-1) - 7 =
- Subtracting a positive number from a negative number makes the result more negative.
- $ (-1) - 7 = -1 - 7 = -8 $
- Answer: $ \boxed{-8} $

---

#### 4. (-18) - 20 =
- Subtracting a positive number from a negative number makes the result more negative.
- $ (-18) - 20 = -18 - 20 = -38 $
- Answer: $ \boxed{-38} $

---

#### 5. (-17) - 1 =
- Subtracting a positive number from a negative number makes the result more negative.
- $ (-17) - 1 = -17 - 1 = -18 $
- Answer: $ \boxed{-18} $

---

#### 6. 13 - (-18) =
- Subtracting a negative number is the same as adding its positive counterpart.
- $ 13 - (-18) = 13 + 18 = 31 $
- Answer: $ \boxed{31} $

---

#### 7. (-9) + (-11) =
- Adding two negative numbers results in a larger negative number.
- $ (-9) + (-11) = -9 - 11 = -20 $
- Answer: $ \boxed{-20} $

---

#### 8. 1 + (-12) =
- Adding a negative number is the same as subtracting its positive counterpart.
- $ 1 + (-12) = 1 - 12 = -11 $
- Answer: $ \boxed{-11} $

---

#### 9. (-8) - 2 =
- Subtracting a positive number from a negative number makes the result more negative.
- $ (-8) - 2 = -8 - 2 = -10 $
- Answer: $ \boxed{-10} $

---

#### 10. 0 - (-10) =
- Subtracting a negative number is the same as adding its positive counterpart.
- $ 0 - (-10) = 0 + 10 = 10 $
- Answer: $ \boxed{10} $

---

#### 11. 38 - (-27) =
- Subtracting a negative number is the same as adding its positive counterpart.
- $ 38 - (-27) = 38 + 27 = 65 $
- Answer: $ \boxed{65} $

---

#### 12. 6 - (-38) =
- Subtracting a negative number is the same as adding its positive counterpart.
- $ 6 - (-38) = 6 + 38 = 44 $
- Answer: $ \boxed{44} $

---

#### 13. 24 - (-31) =
- Subtracting a negative number is the same as adding its positive counterpart.
- $ 24 - (-31) = 24 + 31 = 55 $
- Answer: $ \boxed{55} $

---

#### 14. (-99) - 88 =
- Subtracting a positive number from a negative number makes the result more negative.
- $ (-99) - 88 = -99 - 88 = -187 $
- Answer: $ \boxed{-187} $

---

#### 15. 4 + (-9) =
- Adding a negative number is the same as subtracting its positive counterpart.
- $ 4 + (-9) = 4 - 9 = -5 $
- Answer: $ \boxed{-5} $

---

#### 16. (-1) + (-10) =
- Adding two negative numbers results in a larger negative number.
- $ (-1) + (-10) = -1 - 10 = -11 $
- Answer: $ \boxed{-11} $

---

#### 17. 50 - (-10) =
- Subtracting a negative number is the same as adding its positive counterpart.
- $ 50 - (-10) = 50 + 10 = 60 $
- Answer: $ \boxed{60} $

---

#### 18. (-60) - 12 =
- Subtracting a positive number from a negative number makes the result more negative.
- $ (-60) - 12 = -60 - 12 = -72 $
- Answer: $ \boxed{-72} $

---

#### 19. (-9) - (-19) =
- Subtracting a negative number is the same as adding its positive counterpart.
- $ (-9) - (-19) = -9 + 19 = 10 $
- Answer: $ \boxed{10} $

---

#### 20. (-11) + (-10) =
- Adding two negative numbers results in a larger negative number.
- $ (-11) + (-10) = -11 - 10 = -21 $
- Answer: $ \boxed{-21} $

---

#### 21. 49 - (-40) =
- Subtracting a negative number is the same as adding its positive counterpart.
- $ 49 - (-40) = 49 + 40 = 89 $
- Answer: $ \boxed{89} $

---

Final Answers:

1. $ \boxed{-9} $
2. $ \boxed{-4} $
3. $ \boxed{-8} $
4. $ \boxed{-38} $
5. $ \boxed{-18} $
6. $ \boxed{31} $
7. $ \boxed{-20} $
8. $ \boxed{-11} $
9. $ \boxed{-10} $
10. $ \boxed{10} $
11. $ \boxed{65} $
12. $ \boxed{44} $
13. $ \boxed{55} $
14. $ \boxed{-187} $
15. $ \boxed{-5} $
16. $ \boxed{-11} $
17. $ \boxed{60} $
18. $ \boxed{-72} $
19. $ \boxed{10} $
20. $ \boxed{-21} $
21. $ \boxed{89} $

---

Boxed Final Answer:

$$
\boxed{
\begin{array}{ccc}
-9 & -4 & -8 \\
-38 & -18 & 31 \\
-20 & -11 & -10 \\
10 & 65 & 44 \\
55 & -187 & -5 \\
-11 & 60 & -72 \\
10 & -21 & 89 \\
\end{array}
}
$$