Solve the Equation: Finding the Missing Number in (?)+(-2)=13

Q: Why do I add 2 when subtracting negative 2?

Subtracting a negative is the same as adding a positive! Think of it this way: if you remove a debt of $2, you actually gain $2. So 13 - (-2) = 13 + 2 = 15.

Q: What if the equation was (?) + 2 = 13 instead?

Then you'd subtract: $ 13 - 2 = 11 $. The key is to do the opposite operation of what's being added to the unknown number.

Q: How do I remember when to add or subtract?

Think: "What do I need to add to get 13?" If I already have (-2), I need to add enough to get from (-2) to 13. Count up: (-2) to 0 is +2, then 0 to 13 is +13, so 2 + 13 = 15!

Q: Why is 15 the only correct answer?

Because 15 + (-2) = 13 is the only combination that works! Try the other options: 12 + (-2) = 10, 13 + (-2) = 11, 14 + (-2) = 12. None equal 13 except 15!

Addition Equations with Negative Numbers

Solve the following problem:

$(?)+(-2)=13$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Complete the missing

00:03 Start from point (13) on the axis in the positive direction (right)

00:08 The number is directed, and negative

00:11 Let's isolate the unknown

00:14 Therefore add 2 to 13, jump 2 in the positive direction (right)

00:24 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

Solve the following problem:

$(?)+(-2)=13$

Step-by-step solution

Let's locate the number 13 on the number line.

Since zero is greater than negative 2, we'll move two steps to the right from the number 13.

The number we've reached is 15:

Final Answer

$15$

Key Points to Remember

Essential concepts to master this topic

Rule: To find missing addend, subtract known addend from sum
Technique: From 13, subtract (-2): 13 - (-2) = 13 + 2 = 15
Check: Substitute back: 15 + (-2) = 13 ✓

Common Mistakes

Avoid these frequent errors

Confusing subtraction of negative numbers
Don't subtract (-2) as 13 - 2 = 11! This ignores the negative sign and gives the wrong answer. Always remember: subtracting a negative number means adding the positive version, so 13 - (-2) = 13 + 2 = 15.

Practice Quiz

Test your knowledge with interactive questions

a is negative number.

b is negative number.

What is the sum of a+b?

FAQ

Everything you need to know about this question

Why do I add 2 when subtracting negative 2?

Subtracting a negative is the same as adding a positive! Think of it this way: if you remove a debt of $2, you actually gain$ 2. So 13 - (-2) = 13 + 2 = 15.

Can I use a number line to solve this?

Absolutely! Start at 13 on the number line. Since you're adding (-2), move 2 steps to the left to reach 11. Wait, that's backwards! The missing number should be 2 steps to the right of 13, which is 15.

What if the equation was (?) + 2 = 13 instead?

Then you'd subtract: $13 - 2 = 11$ . The key is to do the opposite operation of what's being added to the unknown number.

How do I remember when to add or subtract?

Think: "What do I need to add to get 13?" If I already have (-2), I need to add enough to get from (-2) to 13. Count up: (-2) to 0 is +2, then 0 to 13 is +13, so 2 + 13 = 15!

Why is 15 the only correct answer?

Because 15 + (-2) = 13 is the only combination that works! Try the other options: 12 + (-2) = 10, 13 + (-2) = 11, 14 + (-2) = 12. None equal 13 except 15!

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