Applying signed number addition to elevation situations: writing equations
About this video
Fiona starts at an elevation of -6 meters and rises M meters to reach 3 meters. The video writes this as -6 + M = 3 and explains why the other equation choices do not match the situation.
You'll be able to
- write an addition equation for a change in elevation using a starting value, a change and an ending value.
- explain why an equation does or does not match a described situation.
Key words
- elevation
- How high or low something is compared with a reference level, like ground or sea level.
- equation
- A statement that two expressions are equal, such as -6 + M = 3.
Transcript
- [Instructor] We're told that Fiona starts at an elevation of negative six meters in an underground subway station. After rising M meters on an escalator, Fiona reaches an elevated walkway at an elevation of three meters. Which equation could represent this situation?
So like always, pause this and have a go at that before we do this together. Okay, before I even look at these choices, let me just see if I can write out what this situation is describing as an equation. So we're starting out at an elevation of negative six meters.
So negative six meters. So we're starting out there and then we rise M meters. So our elevation is going to go up by M meters. And then after we rise by M meters, we're at an elevation of positive three meters, so is equal to three. So let's see if any of these choices are exactly what I just wrote.
So if I look here, it actually looks like choice C is exactly what I wrote. We started at negative six, we added M meters to our elevation, and we got to positive three. So I like choice C here. But we could validate that these other ones don't make sense. This would mean that I started at three, I went down by M meters and I got to six.
So this one actually would've been an equivalent equation if there was a negative six here, but it still wouldn't have obviously described the way the question was written. So we'd rule that one out. Negative six. This is implying that we started at negative six meters.
We added three meters to our altitude and we got to M. That's not what happened. And this implies that we started at three and we added M meters and somehow we got to negative six, but we're saying we're rising M meters. So I do not like that one.
Video © Khan Academy, used under CC BY-NC-SA. Watch on Khan Academy. Puzzicle is not affiliated with Khan Academy.