Matching addition equations with rational numbers to real-world situations
About this video
The video asks which situation matches x + (-9) = -15. It checks a club's account balance, a cave explorer descending 9 meters, and a football team moving backward, and finds that only the cave explorer (start at x, go down 9, end at -15) fits.
You'll be able to
- explain that adding -9 is the same as subtracting 9.
- match an addition equation with rational numbers to a real-world situation.
- explain why a situation does not match an equation.
Key words
- relative to sea level
- Measured up or down from sea level, which counts as zero.
- descending
- Going down, which lowers an elevation.
Transcript
- [Instructor] We're asked, "Which situation could be represented by the equation x plus negative 9 is equal to negative 15?" So pause this video and figure out, and we are only going to pick one answer. All right, so choice A, the Latin club's account balance was x dollars.
After spending $9, so spending, I would subtract from there, the balance was 15, is equal to 15. So I would get x minus 9 is equal to 15, not x. x plus negative 9 could be interpreted as x minus 9, but this gets us to negative 15 so I don't like this choice. A cave explorer's elevation was x meters relative to sea level, okay?
After descending 9 meters, so they're going down 9 meters, the explorer's elevation was negative 15 meters, negative 15 meters. Well, what I just did right over here looks an awful lot like that. The only difference is instead of saying plus negative 9, here I just say minus 9.
So I like this choice, but let's look at choice C just to make sure. A football team's position relative to midfield was negative 15 yards, all right? After moving 9 yards backward, I'm assuming backward is negative, is negative, so minus 9, the position was x.
So this is going to be equal to x. So this is how I would interpret this and even if I were to algebraically manipulate this and add 9 to both sides, I would get negative 15 is equal to x plus 9, which is not what we have here. Here we have x plus negative 9, not x plus 9.
So, I would rule this one out as well.
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