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## Algebra (all content)

### Course: Algebra (all content)>Unit 3

Lesson 11: Interpreting linear functions and equations

# Linear equations word problems: volcano

Sal finds the y-intercept and the slope of a linear relationship representing someone climbing a volcano. He then interprets what the y-intercept and the slope mean in that context. Created by Sal Khan.

## Want to join the conversation?

• Why did Sal move the elevations to the right of the times?
• Because usually in math and physics we like to read a time first, then what the value is (here the elevation) at that given time.

Like for temperatures, you want to know for a given time how hot or cold something is.
• what does relative elevation mean?
• "relative" comes from the past tense of "referre" (refer) in Latin, so it means "with reference to", here "compared to" the top of the volcano. "-24 meters" means 24 meters less (lower) than the top of the volcano.
• How can I determine which data is dependent and which is independent?
• Well, you just have to use your logic. Let's say the amount of days you have car insurance and the money you owe them. In this case, the dependent is the money you owe them, because it is dependent on the amount of days you have it. When you raise the days, you raise the money. Another example is candles you sell and money you make. The dependent would be money you make, and independent would be candles you sell.
• Do you need to use a table for this?
• You don't need to, but it greatly helps if you do.
• i somehow understand what sal is explaining but mange to solve none of the problems correctly .. what should i do?
• Perhaps if you show an sample of your work, we can analyze what step you took wrong.
• What does 'e' as function of time't' means?
• It means you have a function named "E" that accepts inputs as values for the variable "t". This is function notation. You may want to search for the lessons on functions notation to get more details on how function notation works.

Hope this helps.
• Does E stand for elevation? In this video?
• Yes, it stands for Zane's elevation relative to the edge of the inside of the volcano in meters.
• I was doing KA exercise (next exercise) and found in the hints this equation. No matter what I do I can't solve for it the same way as whomever did it. I tried to solve for the Petunias, but my resulted equation never matched theirs(KA's). help!

http://imgur.com/a/BApJF
• I'm going to use "m" for money and "p" for petunias.
m - 5 = -0.25(p - 8)
Distribute: m - 5 = -0.25p + 2
Subtract 2: m - 7 = -0.25p
Divide by -0.25: m/(-0.25) -7/(-0.25)
Note: m/(-0.25) = -4m; and -7/(-0.25) = + 28
This give yous: -4m + 28 = p

hope this helps.