# What type of correlation would you expect between the number of minutes a candle burns and the height of the candle?

Asked by sillymichelleyoung (217) December 21st, 2008

a. positive
b. negative
c. none
d. equal

Would it be “d” ? I’m not sure. This is my friend’s algebra 2 homework, and I really do not know the answer to this.

Could you please explain why if you know this too??

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This seems like a rate question.

tinyfaery (41412)

It is likely a linear relationship so I would say D.

critter1982 (4120)

thanks critter!

it would be a, it is linear, the taller the candle, the longer it burns…if you graph it, say a 1in candle burns 1 hour and a 2in candle burns 2 hours, so on and so forth, if you graph the points (1,1),(2,2),..., you get a positive correlation because the rate is increasing.

miasmom (3490)

sorry, the rate isn’t increasing, it is positive

miasmom (3490)

It depends on how you interpret the question. I thought about it as “As the number of minutes the candle burns [read as “is burning”] the height of the candle will decrease”. Which would make it negative. If “burns” is in the present tense (ie “The log burns” ) then to me, it’s negative.

Perchik (4954)

yes, that is true, if it is burning 5 minutes and it is 10 inches, 10 minutes and it is 9 inches…you would graph (5, 10) (10, 9) ...so on and so forth and in that case it would be a negative correlation, so you are correct it does depend on how you interpret the question. :)

miasmom (3490)

being an algebra teacher, I’m pretty sure the book wants A as the correct answer, but you can definitely argue either A or B.

miasmom (3490)

But in a linear relationship isn’t the correlation equal. 1 to 1, 2 to 2, 3 to 3. Perhaps I am interpreting it wrong.

critter1982 (4120)

the rate is equal or constant, but the correlation is positive or negative in this case. The easiest way to see it is on a graph, what is the slope of the graph…

And the more I think about it, B makes more sense from perchiks response.

miasmom (3490)

@critter Linear means that the rate is constant. Before burning, the candle is at 10 inches. After 5 minutes the candle is at 8 inches. After 10 minutes, the candle is at 6 inches. [For every 5 minutes, the candle decreases by 2 inches]. That would be a linear relationship, because your graph would be something like height = 10 – 2/5(time)

Yes the example candle burns way too fast haha, just an example to illustrate the point

[Not to confuse anyone, but I don’t think it would actually be a linear relationship. If it was a pillar candle, the first time it burns it will lose some height, but after that its feeding off of the already melted wax, thus not shortening very much at all. Which would be some kind of quadratic relationship. If it was a long skinny candle, it might be linear. Regardless, it’s going to be a negative relationship. For every minute the candle burns, it will get shorter. Whether or not “shorter” is constant depends on the linearity of it.]

Perchik (4954)

or