Solve -15 + 3 Using Number Line: Step-by-Step Solution

Integer Addition with Number Line Visualization

15+3= -15+3= -6-6-6-5-5-5-4-4-4-3-3-3-2-2-2-1-1-1000111222333-7-7-7-15-15-15-14-14-14-13-13-13-12-12-12-11-11-11-10-10-10-9-9-9-8-8-8

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 The number is directed and negative
00:08 The negative direction on the axis is left, so we'll take 15 left
00:25 The number is directed and positive
00:28 The positive direction on the axis is right, so we'll take 3 right
00:37 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

15+3= -15+3= -6-6-6-5-5-5-4-4-4-3-3-3-2-2-2-1-1-1000111222333-7-7-7-15-15-15-14-14-14-13-13-13-12-12-12-11-11-11-10-10-10-9-9-9-8-8-8

2

Step-by-step solution

Let's locate negative 15 on the number line.

Since negative 15 is less than 0, we will move fifteen steps to the left of zero, where each step represents one whole number as follows:

-6-6-6-5-5-5-4-4-4-3-3-3-2-2-2-1-1-1000111222333-7-7-7-15-15-15-14-14-14-13-13-13-12-12-12-11-11-11-10-10-10-9-9-9-8-8-8

Now let's look at the operation in the exercise.

Since the operation is +3 +3

And the number 3 is greater than 0, we will move three steps to the right from negative 15, where each step represents one whole number as follows:

-6-6-6-5-5-5-4-4-4-3-3-3-2-2-2-1-1-1000111222333-7-7-7-15-15-15-14-14-14-13-13-13-12-12-12-11-11-11-10-10-10-9-9-9-8-8-8

We can see that the number we reached is negative 12.

3

Final Answer

12 -12

Key Points to Remember

Essential concepts to master this topic
  • Starting Point: Locate the first number (-15) on the number line
  • Movement Rule: Move right for positive numbers: -15 + 3 means 3 steps right
  • Verification: Count the steps: -15 → -14 → -13 → -12 equals -12 ✓

Common Mistakes

Avoid these frequent errors
  • Moving in the wrong direction when adding positive numbers
    Don't move left when adding +3 to -15 = gives -18 instead! Adding positive numbers always means moving right on the number line, even when starting from a negative number. Always move right for addition of positive values.

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 move right when adding a positive number to a negative number?

+

Adding means increasing the value, which always moves right on the number line. Even though -15 is negative, adding +3 makes it less negative (closer to zero), so you move toward the positive direction.

How do I remember which direction to move?

+

Use this rule: Addition = Right, Subtraction = Left. When you see +3, always move 3 steps to the right, regardless of where you start!

What if I'm adding two negative numbers?

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If you're adding a negative number like 15+(3) -15 + (-3) , then you move left because you're actually subtracting. The negative sign changes the direction!

Can I solve this without drawing the number line?

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Yes! Think of it as: -15 + 3 = -15 + 3 = -12. But the number line helps you visualize why this works and builds better number sense.

Why is the answer still negative?

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Because |-15| > |3|. When you start with a bigger negative number and add a smaller positive number, the result stays negative. You need to add more than 15 to make it positive!

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