In the image provided, the problem asks the student to find the mistake in the process of simplifying the expression:

$-20 - 5 + 4 - (-1)$

The steps shown are:

1. $-20 - 5 + 4 - (-1)$
2. $-20 + 5 + 4 + 1$
3. Becomes $-10$

Mistake Explanation:

In step 2, the operation for $-5$ has been incorrectly changed to $+5$, which is a mistake.

Here's the correct way to solve it:

1. Start with: $-20 - 5 + 4 - (-1)$
2. Simplify the double negative: $-(-1)$ becomes $+1$, so the expression becomes $-20 - 5 + 4 + 1$
3. Combine the terms step by step:
   • $-20 - 5 = -25$
   • $-25 + 4 = -21$
   • $-21 + 1 = -20$

So the correct final result should be $-20$, not $-10$.

Do you have any questions or want more details?

Here are some related questions to expand on this:

1. What is the rule for handling double negatives in subtraction?
2. How do we apply the order of operations to addition and subtraction of integers?
3. How can we simplify complex integer expressions more effectively?
4. Why is it important to combine terms carefully when simplifying expressions?
5. What are some common mistakes when working with negative numbers?

Tip: Always pay close attention to signs when adding or subtracting integers, especially when there are negative signs involved!