# Thread: Help with the inverse of a exponential decay (i think?) graph

1. ## Help with the inverse of a exponential decay (i think?) graph

Hi, I'm new here, I also don't know if this is in the right section.
I'm not looking for anyone to fully answer this, I just am wondering what do to with it basically. I know the core ideas about exponential graphs, y = yi * (1 + r)^x where yi is initial value and x is time. but its clear that the graph below has to be an inverse. something around the lines of y = (log x)/(log .99) or something...

yea, i'm really lost. my ultimate question is questiong #3 in the picture below,
how would i find an equation or model to represent the two curves below?
Thanks and sorry again if this is in the wrong section.

2. ## Re: Help with the inverse of a exponential decay (i think?) graph

Originally Posted by tbracket
Hi, I'm new here, I also don't know if this is in the right section.
I'm not looking for anyone to fully answer this, I just am wondering what do to with it basically. I know the core ideas about exponential graphs, y = yi * (1 + r)^x where yi is initial value and x is time. but its clear that the graph below has to be an inverse. something around the lines of y = (log x)/(log .99) or something...

yea, i'm really lost. my ultimate question is questiong #3 in the picture below,
how would i find an equation or model to represent the two curves below?
Thanks and sorry again if this is in the wrong section.

In item one, I found that the coal would decrease linearly at a rate of y = -5x + 2500. I don't know if that helps

3. ## Re: Help with the inverse of a exponential decay (i think?) graph

You'ld better take a harder look at those charts. That is the amount of coal remaining in the resevoir. They don't much look linear.

Example:

1st year usage = 10
Available for year 2= 100 - 10 = 90
2nd year usage = 10 * 1.03 = 10.3 -- A 3% increase
Available for year 3 = 90 - 10.3 = 79.7
3rd year usage = 10 * 1.03^2 = 10.609
Available for year 3 = 79.7 - 10.609 = 69.091
4th year usage = 10 * 1.03^3 = 10.927
Available for year 4 = 69.091 - 10.927 = 58.164

There is nothing linear about it.

The USAGE is growing exponentially. There should not be any straight lines associated with this model.