Solve the Equation: Finding the Missing Number in 9 + (?) = -1

Q: Why is the answer negative when I'm adding?

When you add a negative number to a positive number, you're actually moving left on the number line! Since 9 + (-10) = -1, the missing number must be negative to make the sum smaller than 9.

Q: How do I use the number line to solve this?

Start at 9 and count how many steps left you need to reach -1. Each step left represents -1, so 10 steps left means the answer is $ -10 $.

Q: Can I check my answer without the number line?

Yes! Just substitute back: $ 9 + (-10) = 9 - 10 = -1 $. If you get the original sum, your answer is correct!

Q: What if I get confused about positive and negative?

Remember: adding a negative number is the same as subtracting a positive number. So $ 9 + (-10) $ equals $ 9 - 10 = -1 $.

Q: Is there a formula for finding the missing addend?

Yes! For any equation $ a + ? = b $, the missing number equals $ b - a $. So for $ 9 + ? = -1 $, calculate $ -1 - 9 = -10 $.

Integer Addition with Negative Results

$9+(?)=-1$

❤️ Continue Your Math Journey!

We have hundreds of course questions with personalized recommendations + Account 100% premium

Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Complete the missing part

00:04 The number is oriented and positive

00:07 The positive direction on the axis is to the right, so we'll take 9 to the right

00:27 This is the desired number, let's find it on the axis

00:31 Let's find its distance from the point (9)

00:36 The direction of movement is to the left (negative)

00:55 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

$9+(?)=-1$

Step-by-step solution

To know how much we need to add to the number 9 to get minus 1, we will count the number of steps between the numbers.

Also, we will pay attention to which direction we moved, if we moved right then the number is positive, if we moved left the number will be negative.

We will locate the number 9, and move left until we reach minus 1, where each step represents one whole number, as follows:

We discover that the number of steps is 10, and since we moved left, the number will be minus 10

Final Answer

$-10$

Key Points to Remember

Essential concepts to master this topic

Rule: To find the missing addend, subtract the known addend from the sum
Technique: Calculate -1 - 9 = -10 using number line movement
Check: Verify that 9 + (-10) = -1 on the number line ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting to find the missing number
Don't think 9 + ? = -1 means you add 9 and 1 = wrong positive answer! This ignores the negative result completely. Always subtract the known addend from the sum: -1 - 9 = -10.

Practice Quiz

Test your knowledge with interactive questions

$$ -5-(-2)= $$

FAQ

Everything you need to know about this question

Why is the answer negative when I'm adding?

When you add a negative number to a positive number, you're actually moving left on the number line! Since 9 + (-10) = -1, the missing number must be negative to make the sum smaller than 9.

How do I use the number line to solve this?

Start at 9 and count how many steps left you need to reach -1. Each step left represents -1, so 10 steps left means the answer is $-10$ .

Can I check my answer without the number line?

Yes! Just substitute back: $9 + (-10) = 9 - 10 = -1$ . If you get the original sum, your answer is correct!

What if I get confused about positive and negative?

Remember: adding a negative number is the same as subtracting a positive number. So $9 + (-10)$ equals $9 - 10 = -1$ .

Is there a formula for finding the missing addend?

Yes! For any equation $a + ? = b$ , the missing number equals $b - a$ . So for $9 + ? = -1$ , calculate $-1 - 9 = -10$ .

🌟 Unlock Your Math Potential

Get unlimited access to all 18 Signed Numbers (Positive and Negative) questions, detailed video solutions, and personalized progress tracking.

📹

Unlimited Video Solutions

Step-by-step explanations for every problem

📊

Progress Analytics

Track your mastery across all topics

🚫

Ad-Free Learning

Focus on math without distractions

No credit card required • Cancel anytime