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## Arithmetic (all content)

### Course: Arithmetic (all content) > Unit 2

Lesson 4: Addition and subtraction within 20- Adding within 20 using place value blocks
- Adding within 20 using ten frames
- Adding 7 + 6
- Adding 8 + 7
- Add within 20 visually
- Add within 20
- Adding with arrays
- Adding with arrays
- Subtracting different ways
- Subtract within 20 using a number line
- Subtract within 20 using place value blocks
- Subtract within 20 using ten frames
- Subtracting 14 - 6
- Subtract within 20 visually
- Subtract within 20
- Find missing number (add and subtract within 20)
- Add & subtract within 20

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# Subtract within 20 using a number line

Sal subtracts 17 - 9 using a number line. Created by Sal Khan.

## Want to join the conversation?

- How can 17 minus 9 also be written as 8=17 minus 9?(1 vote)
- 8 is the
**difference**of 17 - 9, so**17-9=8 is also 8=17-9 or 9=17-8**(2 votes)

## Video transcript

- [Instructor] We are told subtract, and they want us to subtract nine from 17 or to figure out what is
equivalent to 17 minus nine. And they give us a hint. They say, "Use the number
line to solve 17 minus nine." So what's going on over here? So on this number line, we can see 17 right over here, and it looks like they took
nine steps to the left. Which makes sense, because
we are subtracting nine. We are taking nine away. So pause this video and using this hint, think about what 17
minus nine is equal to. All right, well, if we start at 17, as we do right over here, and if we were to take nine
steps back, where do we end up? Well, let's see. One step, two steps, three steps, four steps, five steps, six steps, seven steps, eight steps, nine steps. Looks like it gets us to, well, it took us seven steps back to get to 10, and it looks like we took two more steps. So this would be nine right over here, and then this is eight. So it looks like 17 minus
nine is equal to eight. Or another way we could write that is eight is equal to 17 minus nine, and we're done.