About this video
This video uses a number line to find 17 - 9. Starting at 17 and taking 9 steps back, 7 steps reach 10 and 2 more reach 8, so 17 - 9 = 8.
You'll be able to
- subtract within 20 by stepping back on a number line.
- break a subtraction into steps that go back to 10 first.
- write a subtraction fact two ways, like 17 - 9 = 8 and 8 = 17 - 9.
Key words
- subtract
- Take some away to find how many are left.
- number line
- A line with numbers in order; moving left means going down.
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.
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