# Missing value addition and subtraction problems with negative numbers | 7th grade | Khan Academy | Summary and Q&A

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May 27, 2015
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## TL;DR

Learn how to add or subtract positive and negative numbers by using number lines.

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### Q: How can I determine the number needed to subtract from a given number to reach a negative value?

To determine the number needed to subtract, start at the given number on a number line and move to the left until you reach the desired negative value. Count the number of steps taken to determine the number to subtract.

### Q: How can I determine the number needed to add to a negative number to reach a positive value?

Start at the negative number on a number line and move to the right until you reach the desired positive value. Count the number of steps taken to determine the number to add.

### Q: Can you explain the process of adding and subtracting negative numbers with an example?

Sure! Let's say you need to find the value of -3 + (-5). Start at -3 on the number line and move 5 steps to the left. You will reach -8. Therefore, -3 + (-5) is equal to -8.

### Q: What is the process for adding a positive number to a negative number?

Start at the negative number on the number line and move to the right by the value of the positive number. Count the number of steps taken to determine the final value.

## Summary & Key Takeaways

• The video explains how to determine the number needed to add or subtract from a given number to reach another number on a number line.

• Examples are provided to demonstrate how to add or subtract positive and negative numbers using number lines.

• The concept is reiterated through various scenarios to help viewers grasp the concept more effectively.